Method of making acrylic acid from hydroxypropionic acid

ABSTRACT

Methods for making acrylic acid, acrylic acid derivatives, or mixtures thereof by contacting a stream containing hydroxypropionic acid, hydroxypropionic acid derivatives, or mixtures thereof with either an active catalyst containing an amorphous and partially-dehydrated phosphate salt or a precursor catalyst containing a crystalline phosphate salt in a reactor with a low corrosion rate are provided.

FIELD OF THE INVENTION

The present invention generally relates to methods of making acrylicacid, acrylic acid derivatives, or mixtures thereof by contacting a gasfeed stream of water vapor and hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof with a catalyst in a reactor.Specifically, the present invention relates to the use of a catalystcontaining an amorphous and partially-dehydrated phosphate salt, and thereactor is a single-layer reactor that contains aluminum, silicon, ormixtures thereof and has a low corrosion rate. Alternatively, thereactor is a bi-layer reactor that has an inner layer and an outerlayer, whereas the inner layer contains aluminum, and has a lowcorrosion rate.

BACKGROUND OF THE INVENTION

Acrylic acid, acrylic acid derivatives, or mixtures thereof are usedtoday in a variety of industrial materials, such as adhesives, binders,coatings, paints, polishes, detergents, flocculants, dispersants,thixotropic agents, sequestrants, and superabsorbent polymers (SAP),which are used in disposable absorbent articles, including diapers andhygienic products. In terms of production process, acrylic acid istypically made today from the two-step catalytic oxidation of propylene,which in turn is produced from fossil resources, such as petroleum ornatural gas. More on the oxidation of propylene to make acrylic acid andother production methods can be found in the Kirk-Othmer Encyclopedia ofChemical Technology, Vol. 1, pgs. 342-369 (5^(th) Ed., John Wiley &Sons, Inc., 2004).

Fossil-derived acrylic acid contributes to greenhouse emissions due toits high content of fossil-derived carbon. Furthermore, the fossilresources are non-renewable, as it takes hundreds of thousands of yearsto form naturally and only a short time to consume. On the other hand,renewable resources refer to materials that are produced via a naturalprocess at a rate comparable to their rate of consumption (e.g., withina 100-year time frame) and can be replenished naturally or viaagricultural techniques. Examples of renewable resources include plants,such as sugar cane, sugar beets, corn, potatoes, citrus fruit, woodyplants, lignocellulose, carbohydrate, hemicellulose, cellulosic waste,animals, fish, bacteria, fungi, and forestry products. As fossilresources become increasingly scarce, more expensive, and potentiallysubject to regulations for CO₂ emissions, there exists a growing needfor non-fossil-derived acrylic acid, acrylic acid derivatives, ormixtures thereof that can serve as an alternative to fossil-derivedacrylic acid, acrylic acid derivatives, or mixtures thereof.

Many attempts have been made over the last 80 years to makenon-fossil-derived acrylic acid, acrylic acid derivatives, or mixturesthereof from renewable resources, such as lactic acid (also known as2-hydroxypropionic acid), lactic acid derivatives (e.g. alkyl2-acetoxy-propionate and 2-acetoxy propionic acid), 3-hydroxypropionicacid, glycerin, carbon monoxide and ethylene oxide, carbon dioxide andethylene, and crotonic acid. From these resources, only lactic acid isproduced today in high yield and purity from sugar (≥90% of theoreticalyield, or equivalently, ≥0.9 g of lactic acid per g of sugar), and witheconomics which could support producing acrylic acid cost competitivelyto fossil-derived acrylic acid. As such, lactic acid or lactate presentsa real opportunity of serving as a feedstock for bio-based acrylic acid,acrylic acid derivatives, or mixtures thereof. Also, 3-hydroxypropionicacid is expected to be produced at commercial scale in a few years, andas such, 3-hydropropionic acid will present another real opportunity ofserving as feedstock for bio-based acrylic acid, acrylic acidderivatives, or mixtures thereof. Sulfate salts; phosphate salts;mixtures of sulfate and phosphate salts; bases; zeolites or modifiedzeolites; metal oxides or modified metal oxides; and supercritical waterare the main catalysts which have been used to dehydrate lactic acid orlactate to acrylic acid, acrylic acid derivatives, or mixtures thereofin the past with varying success.

For example, U.S. Pat. No. 4,786,756 (issued in 1988), describes thevapor phase dehydration of lactic acid or ammonium lactate to acrylicacid using aluminum phosphate (AlPO₄) treated with an aqueous inorganicbase as a catalyst in a Pyrex reactor. The '756 patent discloses amaximum yield of acrylic acid of 43.3% when lactic acid was fed into thereactor at approximately atmospheric pressure, and a respective yield of61.1% when ammonium lactate was fed into the reactor. In both examples,acetaldehyde was produced at yields of 34.7% and 11.9%, respectively,and other side products were also present in large quantities, such aspropionic acid, CO, and CO₂. Omission of the base treatment causedincreased amounts of the side products. Another example is Hong et al.,Appl. Catal. A: General 396:194-200 (2011), who developed and testedcomposite catalysts made with Ca₃(PO₄)₂ and Ca₂(P₂O₇) salts with aslurry-mixing method. The catalyst with the highest yield of acrylicacid from methyl lactate was the 50%-50% (by weight) catalyst. Ityielded 68% acrylic acid, about 5% methyl acrylate, and about 14%acetaldehyde at 390° C. in a Pyrex reactor. When the feed changed frommethyl lactate to lactic acid, the same catalyst achieved 54% yield ofacrylic acid, 14% yield of acetaldehyde, and 14% yield of propionicacid. Prof. D. Miller's group at Michigan State University (MSU)published many papers on the dehydration of lactic acid or lactic acidesters to acrylic acid and 2,3-pentanedione, such as Gunter et al., J.Catalysis 148:252-260 (1994); and Tam et al., Ind. Eng. Chem. Res.38:3873-3877 (1999). The best acrylic acid yields reported by the groupwere about 33% when lactic acid was dehydrated at 350° C. over lowsurface area and pore volume silica impregnated with NaOH in a Pyrexreactor. In the same experiment, the acetaldehyde yield was 14.7% andthe propionic acid yield was 4.1%. Examples of other catalysts tested bythe group were Na₂SO₄, NaCl, Na₃PO₄, NaNO₃, Na₂SiO₃, Na₄P₂O₇, NaH₂PO₄,Na₂HPO₄, Na₂HAsO₄, NaC₃H₅O₃, NaOH, CsCl, Cs₂SO₄, KOH, CsOH, and LiOH. Inall cases, the above referenced catalysts were tested as individualcomponents, not in mixtures. Finally, the group suggested that the yieldto acrylic acid is improved and the yield to the side products issuppressed when the surface area of the silica support is low, reactiontemperature is high, reaction pressure is low, and residence time of thereactants in the catalyst bed is short. Finally, the Chinese patentapplication 200910054519.7 discloses the use of ZSM-5 molecular sievesmodified with aqueous alkali (such as NH₃, NaOH, and Na₂CO₃) or aphosphoric acid salt (such as NaH₂PO₄, Na₂HPO₄, LiH₂PO₄, LaPO₄, etc.).The best yield of acrylic acid achieved in the dehydration of lacticacid was 83.9%, however that yield was achieved at very long residencetimes.

Therefore, the manufacture of acrylic acid, acrylic acid derivatives, ormixtures thereof from lactic acid or lactate by processes, such as thosedescribed in the literature noted above, has demonstrated: 1) yields ofacrylic acid, acrylic acid derivatives, or mixtures thereof notexceeding 70% at short residence times; 2) low selectivities of acrylicacid, acrylic acid derivatives, or mixtures thereof, i.e., significantamounts of undesired side products, such as acetaldehyde,2,3-pentanedione, propionic acid, CO, and CO₂; 3) long residence timesin the catalyst beds; 4) catalyst deactivation in short time on stream(TOS); and 5) operations in Pyrex reactors. The side products candeposit onto the catalyst resulting in fouling, and premature and rapiddeactivation of the catalyst. Further, once deposited, these sideproducts can catalyze other undesired reactions, such as polymerizationreactions. Aside from depositing on the catalysts, these side products,even when present in only small amounts, impose additional costs inprocessing acrylic acid (when present in the reaction product effluent)in the manufacture of SAP, for example. These deficiencies of the priorart processes and catalysts render them commercially non-viable.

Accordingly, there is a need for methods of making acrylic acid, acrylicacid derivatives or mixtures thereof from hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof with high yield,selectivity, and efficiency (i.e., short residence time); high longevitycatalysts; and in industrially-relevant reactors with low corrosionrates.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof is provided. Themethod comprises contacting a gas feed stream comprising water vapor andhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof with a catalyst in a single-layer reactor at a temperature, awater partial pressure, a Gas Hourly Space Velocity (GHSV), and a WeightHourly Space Velocity (WHSV) to dehydrate said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof, resulting in theproduction of acrylic acid, acrylic acid derivatives, or mixturesthereof; wherein said catalyst comprises a phosphate salt comprising acation and an anion represented by the empirical formula[H_(2(1−x))PO_((4−x))]⁻; wherein x is any real number greater than orequal to 0 and less than or equal to 1; wherein said water partialpressure is equal to or greater than about 0.4 bar; wherein saidsingle-layer reactor comprises a wall, an outer surface, and an innersurface; wherein said wall is made from a wall material, has a wallthickness, and extends from said outer surface to said inner surface;wherein said wall material comprises aluminum in an amount between about1 wt % and about 50 wt %; wherein said inner surface is in contact withsaid catalyst; and wherein said single-layer reactor has a corrosionrate lower than about 1.3 millimeters per year (mm/y) during saiddehydration.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof is provided.The method comprises contacting a gas feed stream comprising water vaporand hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof with a catalyst in a single-layer reactor at atemperature, a water partial pressure, a GHSV, and a WHSV to dehydratesaid hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof, resulting in the production of acrylic acid, acrylicacid derivatives, or mixtures thereof; wherein said catalyst comprises aphosphate salt comprising a cation and an anion represented by theempirical formula [H_(2(1−x))PO_((4−x))]⁻; wherein x is any real numbergreater than or equal to 0 and less than or equal to 1; wherein saidwater partial pressure is equal to or greater than about 0.4 bar;wherein said single-layer reactor comprises a wall, an outer surface,and an inner surface; wherein said wall is made from a wall material,has a wall thickness, and extends from said outer surface to said innersurface; wherein said wall material comprises silicon in an amountbetween about 1 wt % and about 50 wt %; and wherein said inner surfaceis in contact with said catalyst; wherein said single-layer reactor hasa corrosion rate lower than about 1.3 mm/y during said dehydration.

In yet another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof is provided.The method comprises contacting a gas feed stream comprising water vaporand hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof with a catalyst in a bi-layer reactor at a temperature,a water partial pressure, a GHSV, and a WHSV to dehydrate saidhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof, resulting in the production of acrylic acid, acrylic acidderivatives, or mixtures thereof; wherein said catalyst comprises aphosphate salt comprising a cation and an anion represented by theempirical formula [H_(2(1−x))PO_((4−x))]⁻; wherein x is any real numbergreater than or equal to 0 and less than or equal to 1; wherein saidwater partial pressure is equal to or greater than about 0.4 bar;wherein said bi-layer reactor comprises an outer layer, an inner layer,an outer surface, an inner surface, and an interface between said outerlayer and said inner layer; wherein said outer layer is made from anouter layer material, has an outer layer thickness, and extends fromsaid interface to said outer surface; wherein said inner layer is madefrom an inner layer material, has an inner layer thickness, and extendsfrom said inner surface to said interface; wherein said inner layermaterial is selected from the group consisting of aluminum, silicon,copper, silver, gold, titanium, tantalum, tungsten, molybdenum,platinum, palladium, zirconium, and mixtures thereof; wherein said innersurface is in contact with said catalyst; and wherein said bi-layerreactor has a corrosion rate lower than about 1.3 mm/y during saiddehydration.

BRIEF DESCRIPTION OF THE DRAWING

While the specification concludes with claims particularly pointing outand distinctly claiming the invention, it is believed that the presentinvention will be better understood from the following description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a typical water partial pressure versus temperature phaseequilibrium diagram of an active dehydration catalyst (amorphous andpartially-dehydrated phosphate salt) and a precursor dehydrationcatalyst (crystalline phosphate salt either fully-hydrated orfully-dehydrated). The triple point is located at the intersection ofthe three phase equilibrium curves. M^(I) is a monovalent cation. Notethat the reported values of the water partial pressure and temperatureare for illustration purposes only.

FIG. 2 is a half cross sectional side view of a tubular packed-bed flowsingle-layer reactor made in accordance with one embodiment of thepresent invention.

FIG. 3 is a half cross sectional side view of a tubular packed-bed flowbi-layer reactor made in accordance with one embodiment of the presentinvention with an inner layer and an outer layer.

FIG. 4 is a schematic of a metallographic technique used by HaynesInternational, Inc. (Kokomo, Ind.) to estimate the corrosion rate ofcoupons exposed to various environments.

DETAILED DESCRIPTION OF THE INVENTION I Definitions

As used herein, the term “fossil-derived” material refers to a materialthat is produced from fossil resources, such as crude oil (petroleum),natural gas, coal, peat, etc.

As used herein, the term “non-fossil-derived” material refers to amaterial that is produced from non-fossil resources. For clarity and forthe purposes of the present invention, the terms “renewable” material,“bio-based” material, “non-petroleum” material, and “non-fossil-derived”material are used interchangeably.

As used herein, the term “renewable” material refers to a material thatis produced from a renewable resource, which is a resource produced viaa natural process at a rate comparable to its rate of consumption (e.g.,within a 100 year time frame). The renewable resource can be replenishednaturally or via agricultural techniques. Non-limiting examples ofrenewable resources include plants (such as sugar cane, beets, corn,potatoes, citrus fruit, woody plants, lignocellulose, hemicellulose, andcellulosic waste), animals, fish, bacteria, fungi, and forestryproducts. These resources can be naturally occurring, hybrids, orgenetically engineered organisms. Fossil resources take longer than 100years to form and thus they are not considered renewable resources.

As used herein, the term “renewable content” refers to the amount ofcarbon from a renewable resource in a material as a percent of theweight (mass) of the total organic carbon in the material, as determinedby ASTM D6866-10 Method B.

As used herein, the term “catalyst” refers to either an active catalystor precursor catalyst.

As used herein, the term “active catalyst” refers to the in-situdehydration catalyst, which is the form of the catalyst present in thereactor during and responsible for the dehydration. The active catalystof the present invention comprises an amorphous and partially-dehydratedphosphate salt with a cation and an anion represented by the empiricalformula [H_(2(1−x))PO_((4−x))]⁻; wherein x is a real number greater than0 and less than 1.

As used herein, the term “precursor catalyst” refers to the pre-reactiondehydration catalyst, which is the form of the catalyst loaded into thereactor and present in the reactor before the dehydration reactionstarts or before a gas feed stream comprising water vapor at a waterpartial pressure and temperature above those of the triple point of thecatalyst contacts the pre-reaction dehydration catalyst. The precursorcatalyst converts to the active catalyst during the dehydration reactionor in the process conditions that can change its physical and chemicalproperties and become an active catalyst. The precursor catalyst of thepresent invention comprises a crystalline phosphate salt with a cationand an anion represented by the empirical formula[H_(2(1−x))PO_((4−x))]⁻; wherein x is 0 (phosphate salt isfully-hydrated and the anion is represented by the molecular formula[H₂PO₄]⁻) or 1 (phosphate salt is fully-dehydrated and the anion isrepresented by the empirical formula [PO₃]⁻).

As used herein, the term “condensed” refers to a crystalline andfully-dehydrated material.

As used herein, the term “triple point” refers to a point in the waterpartial pressure versus temperature phase equilibrium diagram of acatalyst, which is the intersection of the three phase boundary curves(also called, equilibrium lines) and where the 3 phases of the catalystcoexist in thermodynamic equilibrium: the 1^(st) phase equilibrium lineseparates the crystalline and fully-dehydrated phase from thecrystalline and fully-hydrated phase of the catalyst; the 2^(nd) phaseequilibrium line separates the crystalline and fully-dehydrated phasefrom the amorphous and partially-dehydrated phase of the catalyst; andthe 3^(rd) phase equilibrium line separates the amorphous andpartially-dehydrated phase from the crystalline and fully-hydrated phaseof the catalyst (see FIG. 1).

As used herein, the term “triple point water partial pressure” refers tothe water partial pressure at the triple point of the catalyst.

As used herein, the term “triple point temperature” refers to thetemperature at the triple point of the catalyst.

As used herein, the term “phosphate salt” refers to a phosphate saltthat is neutrally-charged.

As used herein, the term “monophosphate” or “orthophosphate” refers toany phosphate salt whose anion, [PO₄]³⁻, is composed of four oxygenatoms arranged in an almost regular tetrahedral array about a centralphosphorus atom.

As used herein, the term “condensed phosphate” refers to any phosphatesalts containing one or several P—O—P bonds generated by corner sharingof PO₄ tetrahedra.

As used herein, the term “polyphosphate” refers to any condensedphosphate with a linear structure; i.e., containing linear P—O—Plinkages by corner sharing of PO₄ tetrahedra leading to the formation offinite chains.

As used herein, the term “cyclophosphate” refers to any condensedphosphate with a cyclic structure.

As used herein, the term “hydrate” refers to a salt (i.e., salt.nH₂O)which has a number of water molecules (i.e., nH₂O) associated with theions within its crystalline structure.

As used herein, the term “monovalent cation” refers to any cation with apositive charge of +1.

As used herein, the term “polyvalent cation” refers to any cation with apositive charge equal to or greater than +2.

As used herein, the term “heteropolyanion” refers to any anion withcovalently bonded XO_(p) and YO_(r) polyhedra, and thus comprises X—O—Yand possibly X—O—X and Y—O—Y bonds; wherein X and Y represent any atoms,and wherein p and r are any positive integers.

As used herein, the term “heteropolyphosphate” refers to anyheteropolyanion; wherein X represents phosphorus (P) and Y representsany other atom.

As used herein, the term “phosphate adduct” refers to any compound withone or more phosphate anions and one or more non-phosphate anions thatare not covalently linked.

As used herein, the term “amorphous” refers to the state of a materialthat lacks the long-range order characteristic of a crystallinematerial. An amorphous material can be either an amorphous solid or aliquid. In the context of the present invention, materials with equal ormore than 50 wt % of amorphous content are considered amorphousmaterials. The amorphous content of a material is determined by anymethod known to those skilled in the art, such as, by way of example andnot limitation, x-ray diffraction (XRD), infrared spectroscopy (IR),Raman spectroscopy, differential scanning calorimetry (DSC), orsolid-state nuclear magnetic resonance (NMR) spectroscopy. As anillustration, in a method based on an XRD technique, the separatecrystalline (I_(C)) and amorphous (I_(A)) contributions to the X-rayscattering pattern are determined using a profile-fitting technique thatdeconvolutes the scattering pattern into the separate contributionsusing Gaussian, Lorentzian, Voigt, or related functions known to thoseskilled in the art. Then, the amorphous content, X_(A), in wt % isdetermined by calculating the ratio between the area of scatteredintensity for the amorphous contribution (I_(A)) and the area of thetotal scattered intensity (crystalline plus amorphous contributions,I_(T)=I_(C)+I_(A)) for a defined Bragg angle range (e.g. 2θ=5° to 50°,Cu-radiation λ=1.54059 Å, in the context of the current invention),i.e., X_(A)=I_(A)/I_(C)+I_(A)×100.

As used herein, the term “crystalline” refers to the state of a materialwhose constituents are arranged in a highly ordered microscopicstructure forming a crystal lattice with long-range order. In thecontext of the present invention, materials with less than 50 wt % ofamorphous content are considered crystalline materials.

As used herein, the term “chemically inert” material refers to amaterial which remains in the same chemical form, under equilibriumconditions, when contacted with another material or materials. In thecontext of the present invention, more than about 90 wt % of thematerial should remain in the same chemical form to be considered a“significantly chemically inert” material and more than about 98 wt % ofthe material should remain in the same chemical form to be considered an“essentially chemically inert” material.

As used herein, the term “antioxidant” refers to a molecule capable ofterminating radical chain processes by either donating a hydrogen atomor the reaction of an olefinic bond to form a stabilized organic radicaland thus terminate radical chain processes. Non-limiting examples ofantioxidants comprise thiols, polyphenols, butylated hydroxy toluene(BHT), and butylated hydroxy anisole (BHA).

As used herein, the terms “LA” refers to lactic acid, “AA” refers toacrylic acid, “AcH” refers to acetaldehyde, and “PA” refers to propionicacid.

As used herein, the term “conversion” in mol % is defined as[hydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof flow rate in (mol/min)−hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof flow rate out(mol/min)]/[hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof flow rate in (mol/min)]×100.

As used herein, the term “yield” in mol % is defined as [product flowrate out (mol/min)/hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof flow rate in (mol/min)]×100.

As used herein, the term “selectivity” in mol % is defined as[Yield/Conversion]×100.

As used herein, the term “total carbon balance” is defined as: [((molcarbon monoxide out+mol carbon dioxide out+mol methane out)+(2×(molacetic acid out+mol acetaldehyde out+mol ethane out+mol ethyleneout))+(3×(mol acrylic acid out+mol propionic acid out+molhydroxypropionic acid out+mol hydroxyacetone out)+(5×mol 2,3pentanedione out)+(6×mol acrylic acid dimer out))/(3×molhydroxypropionic acid in)]×100. If hydroxypropionic acid derivative isused instead of hydroxypropionic acid, the above formula needs to beadjusted according to the number of carbon atoms in the hydroxypropionicacid derivative.

As used herein, the term “Gas Hourly Space Velocity” or “GHSV” in h⁻¹ isdefined as 60×[Total gas flow rate (mL/min)/precursor catalyst empty bedvolume (mL)]. The total gas flow rate is calculated under StandardTemperature and Pressure conditions (STP; 0° C. and 1 bar).

As used herein, the term “Weight Hourly Space Velocity” or “WHSV” in h⁻¹is defined as 60×[Total LA flow rate (g/min)/precursor catalyst weight(g)]. For the purpose of this definition, the precursor catalyst weightincludes only the weight of the crystalline phosphate salt and does notinclude the weight of any inert support.

As used herein, the term “Liquid Hourly Space Velocity” or “LHSV” in h⁻¹is defined as 60×[Total liquid flow rate (mL/min)/precursor catalystempty bed volume (mL)]. For the purpose of this definition, theprecursor catalyst weight includes only the weight of the crystallinephosphate salt and does not include the weight of any inert support.

II Active Catalysts for the Dehydration of Hydroxypropionic Acid or itsDerivatives to Acrylic Acid or its Derivatives

Unexpectedly, it has been found that active catalysts comprising anamorphous and partially-dehydrated phosphate salt can dehydratehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereofwith: 1) high yield and selectivity (i.e., low amount and few sideproducts), and efficiency (i.e., short residence time); 2) highlongevity catalysts; and 3) in industrially-relevant reactors with lowcorrosion rates. As a non-limiting example, the amorphous andpartially-dehydrated phosphate salt can be formed reversibly when acrystalline phosphate salt (e.g. precursor catalyst with molar ratio ofphosphorus to cations of about 1) is contacted with water vapor at waterpartial pressure and temperature above the triple point of the catalyst.The applicants also found unexpectedly, that in order to dehydratehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof to acrylic acid, acrylic acid derivatives, or mixtures thereof,the active catalyst of the present invention needs to be in the presenceof sufficient water vapor, contrary to the common belief in the art thatdehydration reactions have to be performed under dry conditions.Although not wishing to be bound by any theory, applicants hypothesizethat the water vapor is required to avoid full dehydration of thedihydrogen monophosphate salt (which is fully-hydrated) to condensedphosphate (which is fully-dehydrated) under operating conditions, thusmaintaining the Brønsted acid sites that are required for either theselective acid-catalyzed dehydration or phosphorylation anddephosphorylation of the hydroxypropionic acid and its derivatives toacrylic acid and its derivatives. The ability of some phosphate salts toundergo partial dehydration at some operating conditions is shown inFIG. 1, where a crystalline and fully-dehydrated polyphosphate salt(M^(I)PO₃)_(n) becomes an amorphous and partially-dehydrated saltM^(I)H_(2(1−x))PO_((4−x)) in a specific range of water partial pressureand temperature and then becomes crystalline again in the form ofdihydrogen monophosphate M^(I)H₂PO₄ as the water partial pressureincreases further or the temperature decreases.

In one embodiment of the present invention, the active catalystcomprises a phosphate salt comprising a cation and an anion representedby the empirical formula [H_(2(1−x))PO_((4−x))]⁻; wherein x is any realnumber greater than 0 and less than 1. In another embodiment of thepresent invention, said phosphate salt is amorphous andpartially-dehydrated.

In one embodiment of the present invention, the active catalystcomprises an amorphous and partially-dehydrated phosphate saltcomprising a cation and an anion represented by the empirical formula[H_(2(1−x))PO_((4−x))]⁻; wherein x is any real number greater than 0 andless than 1. Non-limiting examples of cations in the phosphate salt aremetallic cations, organo-metallic cations, ammonium, substitutedammonium, oxycations, and other cations known by those skilled in theart. Non-limiting examples of substituted ammonium and other cations areisopropylammonium, ethylenediammonium, sarcosinium, L-histidinium,glycinium, and 4-aminopyridinium. Non-limiting examples of oxycationsare pervanadyl and vanadyl ions. In another embodiment of the presentinvention, said cation is a monovalent cation. Non-limiting examples ofmonovalent cations are cations of alkali metals, organo-metalliccations, ammonium, substituted ammonium, oxycations (e.g. pervanadyl),and other cations known by those skilled in the art. In yet anotherembodiment of the present invention, said monovalent cation is selectedfrom the group consisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, andmixtures thereof. In even yet another embodiment of the presentinvention, said monovalent cation is selected from the group consistingof K⁺, Rb⁺, Cs⁺, and mixtures thereof. In one embodiment of the presentinvention, said monovalent cation is selected from the group consistingof K⁺, Cs⁺, and mixtures thereof. In another embodiment of the presentinvention, said phosphate salt is amorphous and partially-dehydrated;wherein said x is any real number greater than 0 and less than 1; andwherein said cation is a monovalent cation selected from the groupconsisting of K⁺, Cs⁺, and mixtures thereof. In yet another embodimentof the present invention, said amorphous and partially-dehydratedphosphate salt is selected from the group consisting ofLiH_(2(1−x))PO_((4−x)), NaH_(2(1−x))PO_((4−x)), KH_(2(1−x))PO_((4−x)),RbH_(2(1−x))PO_((4−x)), CsH_(2(1−x))PO_((4−x)), any of their hydrateforms, and mixtures thereof; wherein x is any real number greater than 0and less than 1. In even yet another embodiment of the presentinvention, said amorphous and partially-dehydrated phosphate salt isKH_(2(1−x))PO_((4−x)); wherein x is any real number greater than 0 andless than 1. In one embodiment of the present invention, said amorphousand partially-dehydrated phosphate salt is CsH_(2(1−x))PO_((4−x));wherein x is any real number greater than 0 and less than 1.

In one embodiment of the present invention, the active catalystcomprises an amorphous and partially-dehydrated phosphate saltconsisting of one or more cations, and one or more phosphate anions;wherein at least one phosphate anion is represented by the empiricalformula [H_(2(1−x))PO_((4−x))]⁻, and wherein x is any real numbergreater than 0 and less than 1. For the purposes of the presentinvention, “one or more cations” refers to different types of cations.In another embodiment of the present invention, said cations aremonovalent cations. In yet another embodiment of the present invention,said monovalent cations are selected from the group consisting of Li⁺,Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, and mixtures thereof. In even yet anotherembodiment of the present invention, said monovalent cations areselected from the group consisting of K⁺, Rb⁺, Cs⁺, and mixturesthereof. In one embodiment of the present invention, said monovalentcations are selected from the group consisting of K⁺, Cs⁺, and mixturesthereof.

In one embodiment of the present invention, the active catalystcomprises an amorphous and partially-dehydrated phosphate saltrepresented by the empirical formula M_(w) ^(I)N_((1−w))^(I)H_(2(1−x))PO_((4−x)); wherein M^(I) and N^(I) are two differentmonovalent cations; wherein x is any real number greater than 0 and lessthan 1; and wherein w is any real number greater than 0 and less than 1.In another embodiment of the present invention, the amorphous andpartially-dehydrated phosphate salt is selected from the groupconsisting of Li_(w) Na_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)K_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)K_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Rb_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)), any of their hydrate forms, andmixtures thereof; wherein x is any real number greater than 0 and lessthan 1; and wherein w is any real number greater than 0 and less than 1.

In one embodiment of the present invention, the active catalystcomprising said amorphous and partially-dehydrated phosphate saltfurther comprises a non-phosphate compound; wherein said non-phosphatecompound is significantly chemically inert to said amorphous andpartially-dehydrated phosphate salt. In another embodiment of thepresent invention, the weight ratio of said amorphous andpartially-dehydrated phosphate salt and said non-phosphate compound isbetween about 1:10 and about 4:1.

In one embodiment of the present invention, said non-phosphate compoundcomprises silicon oxide (also called silica; SiO₂). In anotherembodiment of the present invention, said non-phosphate compoundconsists essentially of silica. In yet another embodiment of the presentinvention, said silica is selected from the group consisting ofamorphous silica (also called herein fused silica or fused quartz),quartz, tridymite, cristobalite, moganite, coesite, and mixturesthereof. In even yet another embodiment of the present invention, saidsilica is amorphous silica. In one embodiment of the present invention,said silica has a specific surface area of less than about 10 m²/g.

In another embodiment of the present invention, said non-phosphatecompound comprises a cation and an anion. Non-limiting examples ofanions in the non-phosphate compounds are arsenates, condensedarsenates, nitrates, sulfates, condensed sulfates, borates, carbonates,chromates, condensed chromates, vanadates, niobates, tantalates,selenates, condensed silicates, condensed aluminates, germanates,condensed germanates, molybdates, condensed molybdates, other monomericoxyanions, polyoxyanions, heteropolyphosphates, such asarsenatophosphates, phosphoaluminates, phosphoborates, phosphochromates,phosphomolybdates, phosphosilicates, phosphosulfates, phosphotungstates,and phosphate adducts, such as phosphate anions with telluric acid,halides, borates, carbonates, nitrates, sulfates, chromates, silicates,oxalates, mixtures thereof, or others that may be apparent to thosehaving ordinary skill in the art.

In one embodiment of the present invention, said amorphous andpartially-dehydrated phosphate salt is selected from the groupconsisting of LiH_(2(1−x))PO_((4−x)), NaH_(2(1−x))PO_((4−x)),KH_(2(1−x))PO_((4−x)), RbH_(2(1−x))PO_((4−x)), CsH_(2(1−x))PO_((4−x)),any of their hydrate forms, and mixtures thereof; wherein x is any realnumber greater than 0 and less than 1, and wherein said non-phosphatecompound is selected from the group consisting of amorphous silica,quartz, and mixtures thereof. In another embodiment of the presentinvention, said amorphous and partially-dehydrated phosphate salt isKH_(2(1−x))PO_((4−x)); wherein x is any real number greater than 0 andless than 1, and wherein said non-phosphate compound is amorphoussilica. In yet another embodiment of the present invention, saidamorphous and partially-dehydrated phosphate salt isCsH_(2(1−x))PO_((4−x)); wherein x is any real number greater than 0 andless than 1, and wherein said non-phosphate compound is amorphoussilica.

In one embodiment of the present invention, said amorphous andpartially-dehydrated phosphate salt is selected from the groupconsisting of Li_(w)Na_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)K_((1−w))H_(2(1−x)) PO_((4−x)),Li_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)K_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Rb_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)), any of their hydrate forms, andmixtures thereof; wherein x is any real number greater than 0 and lessthan 1; wherein w is any real number greater than 0 and less than 1, andwherein said non-phosphate compound is selected from the groupconsisting of amorphous silica, quartz, and mixtures thereof.

In one embodiment of the present invention, said non-phosphate compoundcomprises a neutrally-charged oxysalt comprising a cation, and anoxyanion selected from the group represented by molecular formulae[H_((a−2b))S_(c)O_((4c−b))]^((2c−a)−) and [Ta_(2d)O_((5d+e))]^(2e−);wherein a and b are positive integers or zero; wherein c, d, and e arepositive integers; wherein (a−2b) is equal to or greater than zero; andwherein (2c−a) is greater than zero. In another embodiment of thepresent invention, said non-phosphate compound further comprises silica.

In one embodiment of the present invention, said cation of said oxysaltis selected from the group consisting of monovalent cation, polyvalentcation, and mixtures thereof. Non-limiting examples of said polyvalentcation of said oxysalt are cations of alkaline earth metals, transitionmetals, post-transition or poor metals, and metalloids; organo-metalliccations, substituted ammonium cations, oxycations (e.g. vanadyl), andother cations known by those skilled in the art. In another embodimentof the present invention, said polyvalent cation of said oxysalt isselected from the group consisting of the cations of the metals Be, Mg,Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Al, Ga, In,Tl, Si, Ge, Sn, Pb, Sb, Bi, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu, and mixtures thereof. In yet another embodiment of thepresent invention, said polyvalent cation of said oxysalt is selectedfrom the group consisting of the cations of the metals Mg, Ca, Sr, Ba,Y, Mn, Al, Er, and mixtures thereof. In even yet another embodiment ofthe present invention, said polyvalent cation of said oxysalt isselected from the group consisting of divalent cations, trivalentcations, tetravalent cations, pentavalent cations, and mixtures thereof.In one embodiment of the present invention, said polyvalent cation ofsaid oxysalt is selected from the group consisting of Be²⁺, Mg²⁺, Ca²⁺,Sr²⁺, Ba²⁺, Sc³⁺, Y³⁺, Ti³⁺, Ti⁴⁺, Zr²⁺, Zr⁴⁺, Hf⁴⁺, V³⁺, V⁴⁺, Nb³⁺,Cr²⁺, Cr³⁺, Mo³⁺, Mo⁴⁺, Mn²⁺, Mn³⁺, Re⁴⁺, Al³⁺, Ga³⁺, In³⁺, Si⁴⁺, Ge⁴⁺,Sn⁴⁺, Pb⁴⁺, Sb³⁺, Sb⁵⁺, Bi³⁺, La³⁺, Ce³⁺, Ce⁴⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺,Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, Lu³⁺, and mixtures thereof. Inanother embodiment of the present invention, said polyvalent cation ofsaid oxysalt is selected from the group consisting of Mg²⁺, Ca²⁺, Sr²⁺,Ba²⁺, Y³⁺, Mn²⁺, Mn³⁺, Al³⁺, Er³⁺, and mixtures thereof. In yet anotherembodiment of the present invention, said polyvalent cation of saidoxysalt is Ba²⁺.

Non-limiting examples of said monovalent cation of said oxysalt arecations of alkali metals. In one embodiment of the present invention,said monovalent cation of said oxysalt is selected from the groupconsisting of the cations of the metals Li, Na, K, Rb, Cs, Ag, Tl, andmixtures thereof. In another embodiment of the present invention, saidmonovalent cation of said oxysalt is selected from the group consistingof the cations of the metals K, Rb, Cs, and mixtures thereof.

In one embodiment of the present invention, said oxyanion of saidoxysalt is selected from the group represented by molecular formulae[SO₄]²⁻, [S₂O₇]²⁻, [HSO₄]¹⁻, [SO₄]²⁻, [HSO₄]⁻, [Ta₂O₆]²⁻; [Ta₂O₇]⁴⁻,[Ta₂O₉]⁸⁻, [Ta₂O₁₀]¹⁰⁻, [Ta₂O₁₁]¹²⁻, [Ta₄O₁₁]²⁻, [Ta₄O₁₅]¹⁰⁻, andmixtures thereof. In another embodiment of the present invention, saidoxyanion of said oxysalt is selected from the group represented bymolecular formulae [SO₄]²⁻, [Ta₂O₆]²⁻, and mixtures thereof.

Non-limiting examples of said oxysalt are sulfates of alkaline-earthmetals, tantalates of alkaline-earth metals, sulfates of mixed alkaliand alkaline earth metals, and tantalates of mixed alkali and alkalineearth metals. In one embodiment of the present invention, said oxysaltis selected from the group consisting of CaSO₄, SrSO₄, BaSO₄,SrK₂(SO₄)₂, SrRb₂(SO₄)₂, Ca₂K₂(SO₄)₃, Ca₂Rb₂(SO₄)₃, Ca₂Cs₂(SO₄)₃,CaTa₄O₁₁, SrTa₄O₁₁, BaTa₄O₁₁, MgTa₂O₆, CaTa₂O₆, SrTa₂O₆, BaTa₂O₆,Mg₂Ta₂O₇, Ca₂Ta₂O₇, Sr₂Ta₂O₇, SrK₂Ta₂O₇, Ba₂Ta₂O₇, Ba₃Ta₂O₆, Mg₄Ta₂O₉,Ca₄Ta₂O₉, Sr₄Ta₂O₉, Ba₄Ta₂O₉, CasTa₂O₁₀, Ca₂KTa₃O₁₀, Ca₂RbTa₃O₁₀,Ca₂CsTa₃O₁₀, Sr₂KTa₃O₁₀, Sr₂RbTa₃O₁₀, Sr₂CsTa₃O₁₀, Mg₅Ta₄O₁₅, Sr₅Ta₄O₁₅,Ba₅Ta₄O₁₅, Sr₂KTa₅O₁₅, Ba₂KTa₅O₁₅, Sr₆Ta₂O₁₁, Ba₆Ta₂O₁₁, any of theirhydrate forms, and mixtures thereof. In another embodiment of thepresent invention, said oxysalt is selected from the group consisting ofCaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆, BaSO₄, BaTa₂O₆, any of their hydrateforms, and mixtures thereof. In yet another embodiment of the presentinvention, said oxysalt is selected from the group consisting of BaSO₄,BaTa₂O₆, any of their hydrate forms, and mixtures thereof.

In one embodiment of the present invention, said amorphous andpartially-dehydrated phosphate salt is selected from the groupconsisting of KH_(2(1−x))O_((4−x)), RbH_(2(1−x))O_((4−x)),CsH_(2(1−x))PO_((4−x)), any of their hydrate forms, and mixturesthereof; wherein x is any real number greater than 0 and less than 1;and wherein said non-phosphate compound is selected from the groupconsisting of CaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆, BaSO₄, BaTa₂O₆, any oftheir hydrate forms, and mixtures thereof. In another embodiment of thepresent invention, said amorphous and partially-dehydrated phosphatesalt is KH_(2(1−x))PO_((4−x)); wherein x is any real number greater than0 and less than 1; and wherein said non-phosphate compound is BaSO₄. Inyet another embodiment of the present invention, said amorphous andpartially-dehydrated phosphate salt is CsH_(2(1−x))PO_((4−x)); wherein xis any real number greater than 0 and less than 1; and wherein saidnon-phosphate compound is BaSO₄.

In even yet another embodiment of the present invention, said amorphousand partially-dehydrated phosphate salt is selected from the groupconsisting of K_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Rb_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)), any of their hydrate forms, andmixtures thereof; wherein x is any real number greater than 0 and lessthan 1; wherein w is any real number greater than 0 and less than 1; andwherein said non-phosphate compound is selected from the groupconsisting of CaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆, BaSO₄, BaTa₂O₆, any oftheir hydrate forms, and mixtures thereof.

In one embodiment of the present invention, said x is equal to about0.8. In another embodiment of the present invention, said x is less thanabout 0.8. In yet another embodiment of the present invention, said x isless than about 0.6. In even yet another embodiment of the presentinvention, said x is less than about 0.5. In one embodiment of thepresent invention, said x is between about 0.1 and about 0.5. In anotherembodiment of the present invention, said x is between about 0.25 andabout 0.45. In yet another embodiment of the present invention, said xis equal to about 0.4. In even yet another embodiment of the presentinvention, said x is equal to about 0.4 and said monovalent cation ofsaid amorphous and partially-dehydrated phosphate salt is Cs⁺.

In one embodiment of the present invention, said w is greater than about0.9. In another embodiment of the present invention, said w is greaterthan about 0.8. In yet another embodiment of the present invention, saidw is less than about 0.2. In even yet another embodiment of the presentinvention, said w is less than about 0.1.

In one embodiment of the present invention, said amorphous andpartially-dehydrated phosphate salt is a hydrate salt. In anotherembodiment of the present invention, said oxysalt is a hydrate salt. Inyet another embodiment of the present invention, said non-phosphatecompound is a hydrate compound. A hydrate salt or compound contains aspecific number of water molecules per formula unit of the salt orcompound. Non-limiting examples of hydrate salts or compounds arehemihydrate, monohydrate, sesquihydrate, dihydrate, trihydrate,tetrahydrate, pentahydrate, hexahydrate, heptahydrate, octahydrate,nonahydrate, nonahydrate, and decahydrate salts or compounds.

In one embodiment of the present invention, said active catalyst furthercomprises an inert support. Non-limiting examples of inert supports aresilica, silicate, alumina, aluminate, aluminosilicate, titania,titanate, zirconia, zirconate, carbon (such as activated carbon,diamond, graphite, or fullerenes), sulfate, phosphate, tantalate, ceria,other metal oxides, and mixtures thereof. In another embodiment of thepresent invention, said inert support consists essentially of silica. Inyet another embodiment of the present invention, said silica is selectedfrom the group consisting of amorphous silica, quartz, tridymite,cristobalite, moganite, coesite, and mixtures thereof. In even yetanother embodiment of the present invention, said silica is amorphoussilica. In one embodiment of the present invention, said silica has aspecific surface area of less than about 10 m²/g. In another embodimentof the present invention, the inert support represents an amount betweenabout 20 wt % and about 90 wt %, based on the total weight of the activecatalyst.

In one embodiment of the present invention, the weight of the amorphousand partially-dehydrated phosphate salt based on the total weight of theactive catalyst is between about 5 wt % and about 90 wt %. In anotherembodiment of the present invention, the weight of the amorphous andpartially-dehydrated phosphate salt based on the total weight of theactive catalyst is between about 8 wt % and about 60 wt %. In yetanother embodiment of the present invention, the weight of the amorphousand partially-dehydrated phosphate salt based on the total weight of theactive catalyst is between about 12 wt % and about 40 wt %. In even yetanother embodiment of the present invention, the weight of the amorphousand partially-dehydrated phosphate salt based on the total weight of theactive catalyst is between about 12 wt % and about 17 wt %. In oneembodiment of the present invention, the weight of the amorphous andpartially-dehydrated phosphate salt based on the total weight of theactive catalyst is between about 26 wt % and about 32 wt %.

In one embodiment of the present invention, the active catalyst consistsof CsH_(2(1−x))PO_((4−x)) and fused silica; wherein the weight of saidCsH_(2(1−x))PO_((4−x)) based on the total weight of the active catalystis about 14 wt %, and wherein x is any real number greater than 0 andless than 1. In another embodiment of the present invention, the activecatalyst consists of CsH_(2(1−x))PO_((4−x)) and fused silica; whereinthe weight of said CsH_(2(1−x))PO_((4−x)) based on the total weight ofthe active catalyst is about 28 wt %, and wherein x is any real numbergreater than 0 and less than 1. In yet another embodiment of the presentinvention, the active catalyst consists of KH_(2(1−x))PO_((4−x)) andfused silica; wherein the weight of said KH_(2(1−x))PO_((4−x)) based onthe total weight of the active catalyst is about 15 wt %, and wherein xis any real number greater than 0 and less than 1. In even yet anotherembodiment of the present invention, the active catalyst consists ofKH_(2(1−x))PO_((4−x)) and fused silica; wherein the weight of saidKH_(2(1−x))PO_((4−x)) based on the total weight of the active catalystis about 30 wt %, and wherein x is any real number greater than 0 andless than 1. In one embodiment of the present invention, the activecatalyst consists of RbH_(2(1−x))PO_((4−x)) and fused silica; whereinthe weight of said RbH_(2(1−x))PO_((4−x)) based on the total weight ofthe active catalyst is about 14 wt %, and wherein x is any real numbergreater than 0 and less than 1. In another embodiment of the presentinvention, the active catalyst consists of RbH_(2(1−x))PO_((4−x)) andfused silica; wherein the weight of said RbH_(2(1−x))PO_((4−x)) based onthe total weight of the active catalyst is about 29 wt %, and wherein xis any real number greater than 0 and less than 1.

The active catalyst of the present invention can be utilized to catalyzeseveral chemical reactions. Non-limiting examples of reactions are:dehydration of lactic acid, lactic acid derivatives, or mixtures thereofto acrylic acid; dehydration of 3-hydroxypropionic acid,3-hydroxypropionic acid derivatives, or mixtures thereof to acrylicacid; dehydration of glycerin to acrolein; isomerization of lactic acidto 3-hydroxypropionic acid in the presence of water; reduction ofhydroxypropionic acid to propionic acid or 1-propanol in the presence ofhydrogen gas; dehydration of aliphatic alcohols to alkenes or olefins;dehydrogenation of aliphatic alcohols to ethers; other dehydrogenations,hydrolyses, alkylations, dealkylations, oxidations, disproportionations,esterifications, cyclizations, isomerizations, condensations,aromatizations, polymerizations; and other reactions that may beapparent to those having ordinary skill in the art.

III Precursor Catalysts for the Dehydration of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives

In one embodiment of the present invention, the precursor catalystcomprises a phosphate salt consisting of one or more cations; whereinthe ratio of the total moles of all cations and the total moles ofphosphorus is about 1. In another embodiment of the present invention,said phosphate salt is selected from the group consisting of crystallineand fully-dehydrated phosphate salt, crystalline and fully-hydratedphosphate salt, and mixtures thereof.

In one embodiment of the present invention, the precursor catalystcomprises a phosphate salt comprising a cation and an anion representedby the empirical formula [H_(2(1−x))PO_((4−x))]⁻; wherein x is 0 or 1.In another embodiment of the present invention, said phosphate salt iscrystalline.

In one embodiment of the present invention, the precursor catalystcomprises a crystalline phosphate salt comprising a cation and an anionrepresented by the empirical formula [H_(2(1−x))PO_((4−x))]⁻; wherein xis 0 or 1. Non-limiting examples of cations are metallic cations,organo-metallic cations, ammonium, substituted ammonium, oxycations, andother cations known by those skilled in the art. Non-limiting examplesof substituted ammonium and other cations are isopropylammonium,ethylenediammonium, sarcosinium, L-histidinium, glycinium, and4-aminopyridinium. Non-limiting examples of oxycations are pervanadyland vanadyl ions. In another embodiment of the present invention, saidcation is a monovalent cation. Non-limiting examples of monovalentcations are cations of alkali metals, organo-metallic cations, ammonium,substituted ammonium, oxycations (e.g. pervanadyl), and other cationsknown by those skilled in the art. In yet another embodiment of thepresent invention, said monovalent cation is selected from the groupconsisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, and mixtures thereof. Ineven yet another embodiment of the present invention, said monovalentcation is selected from the group consisting of K⁺, Rb⁺, Cs⁺, andmixtures thereof. In one embodiment of the present invention, saidmonovalent cation is selected from the group consisting of K⁺, Cs⁺, andmixtures thereof. In another embodiment of the present invention, saidphosphate salt is crystalline; wherein said x is 0 or 1; and whereinsaid cation is a monovalent cation selected from the group consisting ofK⁺, Cs⁺, and mixtures thereof. In yet another embodiment of the presentinvention, said crystalline phosphate salt is selected from the groupconsisting of LiH_(2(1−x))PO_((4−x)), NaH_(2(1−x))PO_((4−x)),KH_(2(1−x))PO_((4−x)), RbH_(2(1−x))PO_((4−x)), CsH_(2(1−x))PO_((4−x)),any of their hydrate forms, and mixtures thereof; wherein x is 0 or 1.In even yet another embodiment of the present invention, saidcrystalline phosphate salt is KH_(2(1−x))PO_((4−x)); wherein x is 0or 1. In one embodiment of the present invention, said crystallinephosphate salt is CsH_(2(1−x))PO_((4−x)); wherein x is 0 or 1.

In one embodiment of the present invention, the precursor catalystcomprises a crystalline phosphate salt consisting of one or morecations, and one or more phosphate anions; wherein at least onephosphate anion is represented by the empirical formula[H_(2(1−x))PO_((4−x))]; wherein x is 0 or 1. For the purposes of thepresent invention, “one or more cations” refers to different types ofcations. In another embodiment of the present invention, said cationsare monovalent cations. In yet another embodiment of the presentinvention, said monovalent cations are selected from the groupconsisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ag⁺, Tl⁺, and mixtures thereof. Ineven yet another embodiment of the present invention, said monovalentcations are selected from the group consisting of K⁺, Rb⁺, Cs⁺, andmixtures thereof. In one embodiment of the present invention, saidmonovalent cations are selected from the group consisting of K⁺, Cs⁺,and mixtures thereof.

In one embodiment of the present invention, the precursor catalystcomprises a crystalline phosphate salt represented by the empiricalformula M_(w) ^(I)N_((1−w)) ^(I)H_(2(1−x))PO_((4−x)); wherein M^(I) andN^(I) are two different monovalent cations; wherein x is 0 or 1; andwherein w is any real number greater than 0 and less than 1. In anotherembodiment of the present invention, the crystalline phosphate salt isselected from the group consisting ofLi_(w)Na_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)K_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)K_((1−w))H_(2(1−x))PO_((4−x)), Na_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)), Na_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Rb_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)), any of their hydrate forms, andmixtures thereof; wherein x is 0 or 1; and wherein w is any real numbergreater than 0 and less than 1.

In one embodiment of the present invention, the precursor catalystcomprising said crystalline phosphate salt further comprises anon-phosphate compound; wherein said non-phosphate compound issignificantly chemically inert to said crystalline phosphate salt. Inanother embodiment of the present invention, the weight ratio of saidcrystalline phosphate salt and said non-phosphate compound is betweenabout 1:10 and about 4:1.

In one embodiment of the present invention, said non-phosphate compoundcomprises silicon oxide (also, called silica; SiO₂). In anotherembodiment of the present invention, said non-phosphate compoundconsists essentially of silica. In yet another embodiment of the presentinvention, said silica is selected from the group consisting ofamorphous silica (also called herein fused silica or fused quartz),quartz, tridymite, cristobalite, moganite, coesite, and mixturesthereof. In even yet another embodiment of the present invention, saidsilica is amorphous silica. In one embodiment of the present invention,said silica has a specific surface area of less than about 10 m²/g.

In another embodiment of the present invention, said non-phosphatecompound comprises an anion and a cation. Non-limiting examples ofanions in the non-phosphate compounds are arsenates, condensedarsenates, nitrates, sulfates, condensed sulfates, borates, carbonates,chromates, condensed chromates, vanadates, niobates, tantalates,selenates, condensed silicates, condensed aluminates, germanates,condensed germanates, molybdates, condensed molybdates, other monomericoxyanions, polyoxyanions, heteropolyphosphates, such asarsenatophosphates, phosphoaluminates, phosphoborates, phosphochromates,phosphomolybdates, phosphosilicates, phosphosulfates, phosphotungstates,and phosphate adducts, such as phosphate anions with telluric acid,halides, borates, carbonates, nitrates, sulfates, chromates, silicates,oxalates, mixtures thereof, or others that may be apparent to thosehaving ordinary skill in the art.

In one embodiment of the present invention, said crystalline phosphatesalt is selected from the group consisting of LiH_(2(1−x))PO_((4−x)),NaH_(2(1−x))PO_((4−x)), KH_(2(1−x))PO_((4−x)), RbH_(2(1−x))PO_((4−x)),CsH_(2(1−x))PO_((4−x)), any of their hydrate forms, and mixturesthereof; wherein x is 0 or 1; and wherein said non-phosphate compound isselected from the group consisting of amorphous silica, quartz, andmixtures thereof. In another embodiment of the present invention, saidcrystalline phosphate salt is KH_(2(1−x))PO_((4−x)); wherein x is 0 or1; and wherein said non-phosphate compound is amorphous silica. In yetanother embodiment of the present invention, said crystalline phosphatesalt is CsH_(2(1−x))PO_((4−x)); wherein x is 0 or 1; and wherein saidnon-phosphate compound is amorphous silica.

In one embodiment of the present invention, said crystalline phosphatesalt is selected from the group consisting ofLi_(w)Na_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)K_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),Li_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)K_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),Na_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Rb_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)), any of their hydrate forms, andmixtures thereof; wherein x is 0 or 1; wherein w is any real numbergreater than 0 and less than 1; and wherein said non-phosphate compoundis selected from the group consisting of amorphous silica, quartz, andmixtures thereof.

In one embodiment of the present invention, said non-phosphate compoundcomprises a neutrally-charged oxysalt comprising a cation, and anoxyanion selected from the group represented by molecular formulae[H_((a−2b))S_(c)O_((4c−b))]^((2c−a)−) and [Ta_(2d)O_((5d+e))]^(2e−);wherein a and b are positive integers or zero; wherein c, d, and e arepositive integers; wherein (a−2b) is equal to or greater than zero; andwherein (2c−a) is greater than zero. In another embodiment of thepresent invention, said non-phosphate compound further comprises silica.

In one embodiment of the present invention, said cation of said oxysaltis selected from the group consisting of monovalent cation, polyvalentcation, and mixtures thereof. Non-limiting examples of said polyvalentcation of said oxysalt are cations of alkaline earth metals, transitionmetals, post-transition or poor metals, and metalloids; organo-metalliccations, substituted ammonium cations, oxycations (e.g. vanadyl), andother cations known by those skilled in the art. In another embodimentof the present invention, said polyvalent cation of said oxysalt isselected from the group consisting of the cations of the metals Be, Mg,Ca, Sr, Ba, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Al, Ga, In,Tl, Si, Ge, Sn, Pb, Sb, Bi, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu, and mixtures thereof. In yet another embodiment of thepresent invention, said polyvalent cation of said oxysalt is selectedfrom the group consisting of the cations of the metals Mg, Ca, Sr, Ba,Y, Mn, Al, Er, and mixtures thereof. In even yet another embodiment ofthe present invention, said polyvalent cation of said oxysalt isselected from the group consisting of divalent cations, trivalentcations, tetravalent cations, pentavalent cations, and mixtures thereof.In one embodiment of the present invention, said polyvalent cation ofsaid oxysalt is selected from the group consisting of Be²⁺, Mg²⁺, Ca²⁺,Sr²⁺, Ba²⁺, Sc³⁺, Y³⁺, Ti³⁺, Ti⁴⁺, Zr²⁺, Zr⁴⁺, Hf⁴⁺, V^(3+,) V^(4+,)Nb³⁺, Cr²⁺, Cr^(3+,) Mo³⁺, Mo⁴⁺, Mn^(2+,) Mn³⁺, Re⁴⁺, Al³⁺, Ga^(3+,)In^(3+,) Si⁴⁺, Ge^(4+,) Sn⁴⁺, Pb⁴⁺, Sb³⁺, Sb⁵⁺, Bi³⁺, La³⁺, Ce³⁺, Ce⁴⁺,Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd^(3+,) Tb^(3+,) Dy³⁺, Ho^(3+,) Er^(3+,)Tm^(3+,) Yb^(3+,) Lu^(3+,) and mixtures thereof. In another embodimentof the present invention, said polyvalent cation of said oxysalt isselected from the group consisting of Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Y³⁺, Mn²⁺,Mn³⁺, Al³⁺, Er³⁺, and mixtures thereof. In yet another embodiment of thepresent invention, said polyvalent cation of said oxysalt is Ba²⁺.

Non-limiting examples of said monovalent cation of said oxysalt arecations of alkali metals. In one embodiment of the present invention,said monovalent cation of said oxysalt is selected from the groupconsisting of the cations of the metals Li, Na, K, Rb, Cs, Ag, Tl, andmixtures thereof. In another embodiment of the present invention, saidmonovalent cation of said oxysalt is selected from the group consistingof the cations of the metals K, Rb, Cs, and mixtures thereof.

In one embodiment of the present invention, said oxyanion of saidoxysalt is selected from the group represented by molecular formulae[SO₄]²⁻, [S₂O₇]²⁻, [HSO₄]¹⁻, [SO₄]²⁻, [HSO₄]⁻, [Ta₂O₆]^(2−,) [Ta₂O₇]⁴⁻,[Ta₂O₉]⁸⁻, [Ta₂O₁₀]¹⁰⁻, [Ta₂O₁₁]¹²⁻, [Ta₄O₁₁]²⁻, [Ta₄O₁₅]¹⁰⁻, andmixtures thereof. In another embodiment of the present invention, saidoxyanion of said oxysalt is selected from the group represented bymolecular formulae [SO₄]²⁻, [Ta₂O₆]²⁻, and mixtures thereof.

Non-limiting examples of said oxysalt are sulfates of alkaline-earthmetals, tantalates of alkaline-earth metals, sulfates of mixed alkaliand alkaline earth metals, and tantalates of mixed alkali and alkalineearth metals. In one embodiment of the present invention, said oxysaltis selected from the group consisting of CaSO₄, SrSO₄, BaSO₄,SrK₂(SO₄)₂, SrRb₂(SO₄)₂, Ca₂K₂(SO₄)₃, Ca₂Rb₂(SO₄)₃, Ca₂Cs₂(SO₄)₃,CaTa₄O₁₁, SrTa₄O₁₁, BaTa₄O₁₁, MgTa₂O₆, CaTa₂O₆, SrTa₂O₆, BaTa₂O₆,Mg₂Ta₂O₇, Ca₂Ta₂O₇, Sr₂Ta₂O₇, SrK₂Ta₂O₇, Ba₂Ta₂O₇, Ba₃Ta₂Os, Mg₄Ta₂O₉,Ca₄Ta₂O₉, Sr₄Ta₂O₉, Ba₄Ta₂O₉, CasTa₂O₁₀, Ca₂KTa₃O₁₀, Ca₂RbTa₃O₁₀,Ca₂CsTa₃O₁₀, Sr₂KTa₃O₁₀, Sr₂RbTa₃O₁₀, Sr₂CsTa₃O₁₀, Mg₅Ta₄O₁₅, Sr₅Ta₄O₁₅,Ba₅Ta₄O₁₅, Sr₂KTa₅O₁₅, Ba₂KTa₅O₁₅, Sr₆Ta₂O₁₁, Ba₆Ta₂O₁₁, any of theirhydrate forms, and mixtures thereof. In another embodiment of thepresent invention, said oxysalt is selected from the group consisting ofCaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆, BaSO₄, BaTa₂O₆, any of their hydrateforms, and mixtures thereof. In yet another embodiment of the presentinvention, said oxysalt is selected from the group consisting of BaSO₄,BaTa₂O₆, any of their hydrate forms, and mixtures thereof.

In one embodiment of the present invention, said crystalline phosphatesalt is selected from the group consisting of KH_(2(1−x))PO_((4−x)),RbH_(2(1−x))PO_((4−x)), CsH_(2(1−x))PO_((4−x)), any of their hydrateforms, and mixtures thereof; wherein x is 0 or 1; and wherein saidnon-phosphate compound is selected from the group consisting of CaSO₄,CaTa₂O₆, SrSO₄, SrTa₂O₆, BaSO₄, BaTa₂O₆, any of their hydrate forms, andmixtures thereof. In another embodiment of the present invention, saidcrystalline phosphate salt is KH_(2(1−x))PO_((4−x)); wherein x is 0 or1; and wherein said non-phosphate compound is BaSO₄. In yet anotherembodiment of the present invention, said crystalline phosphate salt isCsH_(2(1−x))PO_((4−x)); wherein x is 0 or 1; and wherein saidnon-phosphate compound is BaSO₄.

In even yet another embodiment of the present invention, saidcrystalline phosphate salt is selected from the group consisting ofK_(w)Rb_((1−w))H_(2(1−x))PO_((4−x)),K_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)),Rb_(w)Cs_((1−w))H_(2(1−x))PO_((4−x)), any of their hydrate forms, andmixtures thereof; wherein x is 0 or 1; wherein w is any real numbergreater than 0 and less than 1; and wherein said non-phosphate compoundis selected from the group consisting of CaSO₄, CaTa₂O₆, SrSO₄, SrTa₂O₆,BaSO₄, BaTa₂O₆, any of their hydrate forms, and mixtures thereof.

In one embodiment of the present invention, said w is greater than about0.9. In another embodiment of the present invention, said w is greaterthan about 0.8. In yet another embodiment of the present invention, saidw is less than about 0.2. In even yet another embodiment of the presentinvention, said w is less than about 0.1.

In one embodiment of the present invention, said crystalline phosphatesalt is a hydrate salt. In another embodiment of the present invention,said oxysalt is a hydrate salt. In another embodiment of the presentinvention, said non-phosphate compound is a hydrate compound. A hydratesalt or compound contains a specific number of water molecules performula unit of the salt or compound. Non-limiting examples of hydratesalts or compounds are hemihydrate, monohydrate, sesquihydrate,dihydrate, trihydrate, tetrahydrate, pentahydrate, hexahydrate,heptahydrate, octahydrate, nonahydrate, nonahydrate, and decahydratesalts or compounds.

In one embodiment of the present invention, said precursor catalystfurther comprises an inert support. Non-limiting examples of inertsupports are silica, silicate, alumina, aluminate, aluminosilicate,titania, titanate, zirconia, zirconate, carbon (such as activatedcarbon, diamond, graphite, or fullerenes), sulfate, phosphate,tantalate, ceria, other metal oxides, and mixtures thereof. In anotherembodiment of the present invention, said inert support consistsessentially of silica. In yet another embodiment of the presentinvention, said silica is selected from the group consisting ofamorphous silica, quartz, tridymite, cristobalite, moganite, coesite,and mixtures thereof. In even another embodiment of the presentinvention, said silica is amorphous silica. In one embodiment of thepresent invention, said silica has a specific surface area of less thanabout 10 m²/g. In another embodiment of the present invention, the inertsupport represents an amount between about 20 wt % and about 90 wt %,based on the total weight of the precursor catalyst.

In one embodiment of the present invention, the weight of thecrystalline phosphate salt based on the total weight of the precursorcatalyst is between about 5 wt % and about 90 wt %. In anotherembodiment of the present invention, the weight of the crystallinephosphate salt based on the total weight of the precursor catalyst isbetween about 8 wt % and about 60 wt %. In yet another embodiment of thepresent invention, the weight of the crystalline phosphate salt based onthe total weight of the precursor catalyst is between about 12 wt % andabout 40 wt %. In even yet another embodiment of the present invention,the weight of the crystalline phosphate salt based on the total weightof the precursor catalyst is between about 12 wt % and about 17 wt %. Inone embodiment of the present invention, the weight of the crystallinephosphate salt based on the total weight of the precursor catalyst isbetween about 26 wt % and about 32 wt %.

In one embodiment of the present invention, the precursor catalystconsists of CsPO₃ and fused silica; wherein the weight of said CsPO₃based on the total weight of the precursor catalyst is about 13 wt %. Inanother embodiment of the present invention, the precursor catalystconsists of CsPO₃ and fused silica; wherein the weight of said CsPO₃based on the total weight of the precursor catalyst is about 26 wt %. Inyet another embodiment of the present invention, the precursor catalystconsists of KPO₃ and fused silica; wherein the weight of said KPO₃ basedon the total weight of the precursor catalyst is about 13 wt %. In evenyet another embodiment of the present invention, the precursor catalystconsists of KPO₃ and fused silica; wherein the weight of said KPO₃ basedon the total weight of the precursor catalyst is about 26 wt %. In oneembodiment of the present invention, the precursor catalyst consists ofRbPO₃ and fused silica; wherein the weight of said RbPO₃ based on thetotal weight of the precursor catalyst is about 13 wt %. In anotherembodiment of the present invention, the precursor catalyst consists ofRbPO₃ and fused silica; wherein the weight of said RbPO₃ based on thetotal weight of the precursor catalyst is about 26 wt %.

In one embodiment of the present invention, the precursor catalystconsists of CsH₂PO₄ and fused silica; wherein the weight of said CsH₂PO₄based on the total weight of the precursor catalyst is about 14 wt %. Inanother embodiment of the present invention, the precursor catalystconsists of CsH₂PO₄ and fused silica; wherein the weight of said CsH₂PO₄based on the total weight of the precursor catalyst is about 28 wt %. Inyet another embodiment of the present invention, the precursor catalystconsists of KH₂PO₄ and fused silica; wherein the weight of said KH₂PO₄based on the total weight of the precursor catalyst is about 15 wt %. Ineven yet another embodiment of the present invention, the precursorcatalyst consists of KH₂PO₄ and fused silica; wherein the weight of saidKH₂PO₄ based on the total weight of the precursor catalyst is about 30wt %. In one embodiment of the present invention, the precursor catalystconsists of RbH₂PO₄ and fused silica; wherein the weight of said RbH₂PO₄based on the total weight of the precursor catalyst is about 14 wt %. Inanother embodiment of the present invention, the precursor catalystconsists of RbH₂PO₄ and fused silica; wherein the weight of said RbH₂PO₄based on the total weight of the precursor catalyst is about 29 wt %.

In one embodiment of the present invention, the precursor catalystcomprises two or more different phosphate compounds selected from thegroup consisting of M_(j) ^(I)(H_((2+i−j))P_(i)O_((3i+1))),(NH₄)_(l)(H_((2+k−1))P_(k)O_((3k+1))), M_(p) ^(I)(H_((m−p))(PO₃)_(m)),(NH₄)_(r)(H_((q−r))(PO₃)_(q)), M_(u)^(I)(H_((t−u))P_((2s+t))O_((5s+3t))),(NH₄)_(α)(H_((w−α))P_((2v+w))O_((5v+3w))), M₂ ^(I), M^(I)OH, M^(I)NO₃,M₂ ^(I) CO₃, and (H(CH₂)_(β)COO)M^(I); wherein M^(I) is a monovalentcation selected from the group consisting of Li⁺, N⁺, K⁺, Rb⁺, Cs⁺, Ag⁺,Tl⁺, and mixtures thereof; wherein i, k, m, q, s, and v are integersgreater than 0; wherein j, l, p, r, u, and α are real numbers equal toor greater than 0; wherein t, w, and β are integers equal to or greaterthan 0; wherein (2+i−j), (2+k−l), (m−p), (q−r), (t−u), and (w−α) areequal to or greater than 0; and wherein the ratio of the total moles ofsaid one or more monovalent cations and the total moles of phosphorus insaid precursor catalyst is about 1.

In another embodiment of the present invention, the precursor catalystcomprises one or more phosphate salts consisting essentially of one ormore monovalent cations, and one or more phosphate anions selected fromthe group represented by molecular formulae [H₂P_(y)O_((3y+1))]^(y−) and[PO₃]_(z) ^(z−); wherein y is any integer equal to or greater than 1 andz is any integer equal to or greater than 3. In the context of thepresent invention, the anion represented by molecular formula [PO₃]_(z)^(z−) can refer either to the anion of cyclophosphate salts or to theanion of long-chain linear polyphosphate salts as described in“Phosphoric Acids and Phosphates, Kirk-Othmer Encyclopedia of ChemicalTechnology” by David R. Gard (published online: 15 Jul. 2005) and“Phosphorus: Chemistry, Biochemistry and Technology” by D. E. C.Corbridge (2013). When the molecular formula [PO₃]_(z) ^(z−) refers tothe anion of long chain polyphosphate salts, the molecular formula isnot precise in that it does not include the minor perturbation of excessnegative charge owing to the two end-group oxygens.

The precursor catalyst of the present invention can be utilized tocatalyze several chemical reactions. Non-limiting examples of reactionsare: dehydration of lactic acid, lactic acid derivatives, or mixturesthereof to acrylic acid; dehydration of 3-hydroxypropionic acid,3-hydroxypropionic acid derivatives, or mixtures thereof to acrylicacid; dehydration of glycerin to acrolein; isomerization of lactic acidto 3-hydroxypropionic acid in the presence of water; reduction ofhydroxypropionic acid to propionic acid or 1-propanol in the presence ofhydrogen gas; dehydration of aliphatic alcohols to alkenes or olefins;dehydrogenation of aliphatic alcohols to ethers; other dehydrogenations,hydrolyses, alkylations, dealkylations, oxidations, disproportionations,esterifications, cyclizations, isomerizations, condensations,aromatizations, polymerizations; and other reactions that may beapparent to those having ordinary skill in the art.

IV Methods of Preparing the Catalyst

In the context of the present invention, the triple point of a phosphatesalt is the temperature and water partial pressure at which three phasesof the phosphate salt (i.e., crystalline and fully-hydrated, crystallineand fully-dehydrated, and amorphous and partially-dehydrated) coexist inthermodynamic equilibrium. By way of example, and not limitation, thetriple point can be located by determining the interception of two (outof three) phase boundary curves in the water partial pressure versustemperature phase equilibrium diagram (see FIG. 1): Curve A: phaseboundary between crystalline and fully-hydrated phosphate salt, andcrystalline and fully-dehydrated phosphate salt, at low temperature andwater partial pressure (e.g. below about 248° C. and 0.85 bar forpotassium phosphate salts, and below about 267° C. and 0.35 bar forcesium phosphate salts); Curve B: phase boundary between crystalline andfully-dehydrated phosphate salt, and amorphous and partially-dehydratedphosphate salt at high temperature and medium water partial pressure(e.g. above about 248° C. and 0.85 bar for potassium phosphate salts,and above about 267° C. and 0.35 bar for cesium phosphate salts); andCurve C: phase boundary between crystalline and fully-hydrated phosphatesalt, and amorphous and partially-dehydrated phosphate salt at hightemperature and high water partial pressure.

The phase boundary curves can be determined by any method known to thoseskilled in the art, such as, by way of example and not limitation,in-situ x-ray diffraction (XRD), thermal analysis (e.g.thermogravimetric analysis, differential thermal analysis, anddifferential scanning calorimetry), Raman spectroscopy, infraredspectroscopy (IR), nuclear magnetic resonance (NMR) spectroscopy, or themethods described in Taninouchi, Y.-k., et al., J. Electrochem. Soc.156:B572-B579 (2009); or Ikeda, A. and Haile, S. M., Solid State Ionics2012, 213:63-71 (2012) (all incorporated herein by reference). As anillustration, in a method based on the in-situ XRD technique, aprecursor catalyst comprising a crystalline phosphate salt is contacted,at high temperature (e.g. 450° C.), with a gas feed stream consisting ofan inert gas (e.g. nitrogen, helium, or air) and water vapor at aspecific water partial pressure until equilibrium is achieved. Then, thetemperature is gradually decreased while monitoring changes on x-raydiffraction patterns, until a phase transition is observed. The sameprocedure is repeated at different water partial pressures and thetransition temperatures are recorded. The water partial pressures (inlogarithmic scale) are plotted against the transition temperatures (inlinear scale) and fitted to the Arrhenius equation (log₁₀(P_(H) ₂_(O))=A+B/T). Finally, the triple point is calculated by determining theinterception point between the two phase boundary curves (i.e., curve Aand curve B in FIG. 1).

The active catalysts of the present invention are the amorphous andpartially-dehydrated phosphate salts that lie between Curves B and C(bifurcated area above the triple point) in the water partial pressureversus temperature phase equilibrium diagram of the catalyst (e.g. FIG.1). These active catalysts can be produced by subjecting precursorcatalysts containing a crystalline phosphate salt that lies either aboveCurves A and C or below Curves A and B in FIG. 1) to sufficienttemperature or water partial pressure or combination of both for thecrystalline phosphate salt to become an amorphous andpartially-dehydrated phosphate salt lying between Curves B and C in thephase equilibrium diagram.

In one embodiment of the present invention, a method of converting aprecursor catalyst comprising a crystalline phosphate salt to an activecatalyst comprising an amorphous and partially-dehydrated phosphate saltcomprises contacting said precursor catalyst with a gas feed streamcomprising water vapor; wherein said contacting is performed at atemperature and water partial pressure sufficient to convert saidcrystalline phosphate salt to said amorphous and partially-dehydratedphosphate salt. In another embodiment of the present invention, a methodof converting a precursor catalyst comprising a crystalline phosphatesalt to an active catalyst comprising an amorphous andpartially-dehydrated phosphate salt comprises contacting said precursorcatalyst with a gas feed stream comprising water vapor, hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof; whereinsaid contacting is performed at a temperature and water partial pressuresufficient to convert said crystalline phosphate salt to said amorphousand partially-dehydrated phosphate salt; and wherein said contactingproduces acrylic acid, acrylic acid derivatives, or mixtures thereoffrom said hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof.

In one embodiment of the present invention, the temperature at whichsaid gas feed stream contacts said precursor catalyst comprising acrystalline phosphate salt is between about 120° C. and about 700° C. Inanother embodiment of the present invention, the temperature at whichsaid gas feed stream contacts said precursor catalyst comprising acrystalline phosphate salt is between about 150° C. and about 500° C. Inyet another embodiment of the present invention, the temperature atwhich said gas feed stream contacts said precursor catalyst comprising acrystalline phosphate salt is between about 300° C. and about 450° C. Ineven yet another embodiment of the present invention, the temperature atwhich said gas feed stream contacts said precursor catalyst comprising acrystalline phosphate salt is between about 325° C. and about 400° C.

In one embodiment of the present invention, the water partial pressurein said gas feed stream is equal to or greater than about 0.4 bar. Inanother embodiment of the present invention, the water partial pressurein said gas feed stream is equal to or greater than about 0.8 bar. Inyet another embodiment of the present invention, the water partialpressure in said gas feed stream is between about 0.4 bar and about 20bar. In even yet another embodiment of the present invention, the waterpartial pressure in said gas feed stream is between about 0.8 bar andabout 16 bar. In one embodiment of the present invention, the waterpartial pressure in said gas feed stream is about 13 bar.

In one embodiment of the present invention, the total pressure of saidgas feed stream is equal to or greater than about 1 bar. In anotherembodiment of the present invention, the total pressure of said gas feedstream is equal to or greater than about 4 bar. In yet anotherembodiment of the present invention, the total pressure of said gas feedstream is between about 4 bar and about 35 bar. In even yet anotherembodiment of the present invention, the total pressure of said gas feedstream is between about 8 bar and about 30 bar. In one embodiment of thepresent invention, the total pressure of said gas feed stream is about26 bar.

In one embodiment of the present invention, a method of converting aprecursor catalyst comprising CsPO₃ or CsH₂PO₄ to an active catalystcomprising an amorphous and partially-dehydrated phosphate saltCsH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidtemperature is about 400° C.; and wherein said water partial pressure isbetween about 3 bar and about 20 bar. In another embodiment of thepresent invention, a method of converting a precursor catalystcomprising CsPO₃ or CsH₂PO₄ to an active catalyst comprising anamorphous and partially-dehydrated phosphate salt CsH_(2(1−x))PO_((4−x))comprises contacting said precursor catalyst with a gas feed streamcomprising water vapor; wherein said contacting is performed at atemperature and a water partial pressure; wherein said temperature isabout 375° C.; and wherein said water partial pressure is between about2 bar and about 10 bar. In yet another embodiment of the presentinvention, a method of converting a precursor catalyst comprising CsPO₃or CsH₂PO₄ to an active catalyst comprising an amorphous andpartially-dehydrated phosphate salt CsH_(2(1−x))PO_((4−x)) comprisescontacting said precursor catalyst with a gas feed stream comprisingwater vapor; wherein said contacting is performed at a temperature and awater partial pressure; wherein said temperature is about 350° C.; andwherein said water partial pressure is between about 1.5 bar and about 5bar. In even yet another embodiment of the present invention, a methodof converting a precursor catalyst comprising CsPO₃ or CsH₂PO₄ to anactive catalyst comprising an amorphous and partially-dehydratedphosphate salt CsH_(2(1−x))PO_((4−x)) comprises contacting saidprecursor catalyst with a gas feed stream comprising water vapor;wherein said contacting is performed at a temperature and a waterpartial pressure; wherein said temperature is about 325° C.; and whereinsaid water partial pressure is between about 1 bar and about 2 bar. Inone embodiment of the present invention, a method of converting aprecursor catalyst comprising CsPO₃ or CsH₂PO₄ to an active catalystcomprising an amorphous and partially-dehydrated phosphate saltCsH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidtemperature is about 300° C.; and wherein said water partial pressure isbetween about 0.7 bar and about 1.2 bar.

In one embodiment of the present invention, a method of converting aprecursor catalyst comprising CsPO₃ or CsH₂PO₄ to an active catalystcomprising an amorphous and partially-dehydrated phosphate saltCsH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidwater partial pressure is about 1 bar; and wherein said temperature isbetween about 300° C. and about 325° C. In another embodiment of thepresent invention, a method of converting a precursor catalystcomprising CsPO₃ or CsH₂PO₄ to an active catalyst comprising anamorphous and partially-dehydrated phosphate salt CsH_(2(1−x))PO_((4−x))comprises contacting said precursor catalyst with a gas feed streamcomprising water vapor; wherein said contacting is performed at atemperature and a water partial pressure; wherein said water partialpressure is about 2 bar; and wherein said temperature is between about325° C. and about 375° C. In yet another embodiment of the presentinvention, a method of converting a precursor catalyst comprising CsPO₃or CsH₂PO₄ to an active catalyst comprising an amorphous andpartially-dehydrated phosphate salt CsH_(2(1−x))PO_((4−x)) comprisescontacting said precursor catalyst with a gas feed stream comprisingwater vapor; wherein said contacting is performed at a temperature and awater partial pressure; wherein said water partial pressure is about 3bar; and wherein said temperature is between about 325° C. and about400° C. In even yet another embodiment of the present invention, amethod of converting a precursor catalyst comprising CsPO₃ or CsH₂PO₄ toan active catalyst comprising an amorphous and partially-dehydratedphosphate salt CsH_(2(1−x))PO_((4−x)) comprises contacting saidprecursor catalyst with a gas feed stream comprising water vapor;wherein said contacting is performed at a temperature and a waterpartial pressure; wherein said water partial pressure is about 10 bar;and wherein said temperature is between about 375° C. and about 500° C.

In one embodiment of the present invention, the weight of said CsPO₃based on the total weight of said precursor catalyst is about 13 wt %.In another embodiment of the present invention, the weight of said CsPO₃based on the total weight of said precursor catalyst is about 26 wt %.

In one embodiment of the present invention, a method of converting aprecursor catalyst comprising KPO₃ or KH₂PO₄ to an active catalystcomprising an amorphous and partially-dehydrated phosphate saltKH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidtemperature is about 400° C.; and wherein said water partial pressure isbetween about 5 bar and about 400 bar. In another embodiment of thepresent invention, a method of converting a precursor catalystcomprising KPO₃ or KH₂PO₄ to an active catalyst comprising an amorphousand partially-dehydrated phosphate salt KH_(2(1−x))PO_((4−x)) comprisescontacting said precursor catalyst with a gas feed stream comprisingwater vapor; wherein said contacting is performed at a temperature and awater partial pressure; wherein said temperature is about 375° C.; andwherein said water partial pressure is between about 4 bar and about 100bar. In yet another embodiment of the present invention, a method ofconverting a precursor catalyst comprising KPO₃ or KH₂PO₄ to an activecatalyst comprising an amorphous and partially-dehydrated phosphate saltKH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidtemperature is about 350° C.; and wherein said water partial pressure isbetween about 3 bar and about 50 bar. In even yet another embodiment ofthe present invention, a method of converting a precursor catalystcomprising KPO₃ or KH₂PO₄ to an active catalyst comprising an amorphousand partially-dehydrated phosphate salt KH_(2(1−x))PO_((4−x)) comprisescontacting said precursor catalyst with a gas feed stream comprisingwater vapor; wherein said contacting is performed at a temperature and awater partial pressure; wherein said temperature is about 325° C.; andwherein said water partial pressure is between about 2 bar and about 20bar. In one embodiment of the present invention, a method of convertinga precursor catalyst comprising KPO₃ or KH₂PO₄ to an active catalystcomprising an amorphous and partially-dehydrated phosphate saltKH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidtemperature is about 300° C.; and wherein said water partial pressure isbetween about 1.5 bar and about 7 bar.

In one embodiment of the present invention, a method of converting aprecursor catalyst comprising KPO₃ or KH₂PO₄ to an active catalystcomprising an amorphous and partially-dehydrated phosphate saltKH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidwater partial pressure is about 2 bar; and wherein said temperature isbetween about 275° C. and about 325° C. In another embodiment of thepresent invention, a method of converting a precursor catalystcomprising KPO₃ or KH₂PO₄ to an active catalyst comprising an amorphousand partially-dehydrated phosphate salt KH_(2(1−x))PO_((4−x)) comprisescontacting said precursor catalyst with a gas feed stream comprisingwater vapor; wherein said contacting is performed at a temperature and awater partial pressure; wherein said water partial pressure is about 4bar; and wherein said temperature is between about 285° C. and about375° C. In yet another embodiment of the present invention, a method ofconverting a precursor catalyst comprising KPO₃ or KH₂PO₄ to an activecatalyst comprising an amorphous and partially-dehydrated phosphate saltKH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidwater partial pressure is about 8 bar; and wherein said temperature isbetween about 300° C. and about 450° C.

In one embodiment of the present invention, the weight of said KPO₃based on the total weight of said precursor catalyst is about 13 wt %.In another embodiment of the present invention, the weight of said KPO₃based on the total weight of said precursor catalyst is about 26 wt %.

In one embodiment of the present invention, a method of converting aprecursor catalyst comprising RbPO₃ or RbH₂PO₄ to an active catalystcomprising an amorphous and partially-dehydrated phosphate saltRbH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidtemperature is about 400° C.; and wherein said water partial pressure isbetween about 4 bar and about 200 bar. In another embodiment of thepresent invention, a method of converting a precursor catalystcomprising RbPO₃ or RbH₂PO₄ to an active catalyst comprising anamorphous and partially-dehydrated phosphate salt RbH_(2(1−x))PO_((4−x))comprises contacting said precursor catalyst with a gas feed streamcomprising water vapor; wherein said contacting is performed at atemperature and a water partial pressure; wherein said temperature isabout 375° C.; and wherein said water partial pressure is between about3 bar and about 50 bar. In yet another embodiment of the presentinvention, a method of converting a precursor catalyst comprising RbPO₃or RbH₂PO₄ to an active catalyst comprising an amorphous andpartially-dehydrated phosphate salt RbH_(2(1−x))PO_((4−x)) comprisescontacting said precursor catalyst with a gas feed stream comprisingwater vapor; wherein said contacting is performed at a temperature and awater partial pressure; wherein said temperature is about 350° C.; andwherein said water partial pressure is between about 2.5 bar and about25 bar. In even yet another embodiment of the present invention, amethod of converting a precursor catalyst comprising RbPO₃ or RbH₂PO₄ toan active catalyst comprising an amorphous and partially-dehydratedphosphate salt RbH_(2(1−x))PO_((4−x)) comprises contacting saidprecursor catalyst with a gas feed stream comprising water vapor;wherein said contacting is performed at a temperature and a waterpartial pressure; wherein said temperature is about 325° C.; and whereinsaid water partial pressure is between about 1.5 bar and about 10 bar.In one embodiment of the present invention, a method of converting aprecursor catalyst comprising RbPO₃ or RbH₂PO₄ to an active catalystcomprising an amorphous and partially-dehydrated phosphate saltRbH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidtemperature is about 300° C.; and wherein said water partial pressure isbetween about 1 bar and about 4 bar.

In one embodiment of the present invention, a method of converting aprecursor catalyst comprising RbPO₃ or RbH₂PO₄ to an active catalystcomprising an amorphous and partially-dehydrated phosphate saltRbH_(2(1−x))PO_((4−x)) comprises contacting said precursor catalyst witha gas feed stream comprising water vapor; wherein said contacting isperformed at a temperature and a water partial pressure; wherein saidwater partial pressure is about 1.5 bar; and wherein said temperature isbetween about 290° C. and about 325° C. In another embodiment of thepresent invention, a method of converting a precursor catalystcomprising RbPO₃ or RbH₂PO₄ to an active catalyst comprising anamorphous and partially-dehydrated phosphate salt RbH_(2(1−x))PO_((4−x))comprises contacting said precursor catalyst with a gas feed streamcomprising water vapor; wherein said contacting is performed at atemperature and a water partial pressure; wherein said water partialpressure is about 3 bar; and wherein said temperature is between about300° C. and about 375° C. In yet another embodiment of the presentinvention, a method of converting a precursor catalyst comprising RbPO₃or RbH₂PO₄ to an active catalyst comprising an amorphous andpartially-dehydrated phosphate salt RbH_(2(1−x))PO_((4−x)) comprisescontacting said precursor catalyst with a gas feed stream comprisingwater vapor; wherein said contacting is performed at a temperature and awater partial pressure; wherein said water partial pressure is about 3bar; and wherein said temperature is between about 325° C. and about400° C. In even yet another embodiment of the present invention, amethod of converting a precursor catalyst comprising RbPO₃ or RbH₂PO₄ toan active catalyst comprising an amorphous and partially-dehydratedphosphate salt RbH_(2(1−x))PO_((4−x)) comprises contacting saidprecursor catalyst with a gas feed stream comprising water vapor;wherein said contacting is performed at a temperature and a waterpartial pressure; wherein said water partial pressure is about 10 bar;and wherein said temperature is between about 375° C. and about 500° C.

In one embodiment of the present invention, the weight of said RbPO₃based on the total weight of said precursor catalyst is about 13 wt %.In another embodiment of the present invention, the weight of said RbPO₃based on the total weight of said precursor catalyst is about 26 wt %.

In one embodiment of the present invention, the method of preparing thecatalyst further comprises molding the particles of said precursorcatalyst before said contacting with said gas feed stream. Non-limitingexamples of molding operations are granulation, agglomeration,compaction, pelleting, and extrusion. In another embodiment of thepresent invention, the method of preparing the catalyst furthercomprises size reduction or grinding of the particles of said precursorcatalyst before said contacting with said gas feed stream. In oneembodiment of the present invention, the method of preparing thecatalyst further comprises sieving the particles of said precursorcatalyst to select a material of specific size distribution before saidcontacting with said gas feed stream. In another embodiment of thepresent invention, the method of preparing the catalyst furthercomprises sieving the particles of said precursor catalyst to a medianparticle size between about 50 μm and about 500 μm. In yet anotherembodiment of the present invention, the method of preparing thecatalyst further comprises sieving the particles of said precursorcatalyst to a median particle size between about 100 μm and about 200μm. In even yet another embodiment of the present invention, the methodof preparing the catalyst further comprises sieving the particles ofsaid precursor catalyst to a particle size between about 106 μm andabout 212 μm.

In one embodiment of the present invention, the active catalyst isprepared via: (a) mixing KH₂PO₄ and amorphous silica in a weight ratiobetween about 2:1 and about 1:8, to produce a precursor catalyst, (b)heating said precursor catalyst between about 200° C. and about 650° C.for about 1 hour to about 12 hours to produce a calcined precursorcatalyst, (c) optionally grinding and sieving said calcined precursorcatalyst to produce a ground calcined precursor catalyst, and (d)contacting said calcined precursor catalyst or said ground calcinedprecursor catalyst with a gas feed stream comprising nitrogen and watervapor; wherein the water partial pressure in said gas feed stream isbetween about 5 bar and about 15 bar; and wherein said contacting isperformed at a temperature between about 325° C. and about 425° C. toproduce said active catalyst.

In another embodiment of the present invention, the active catalyst isprepared via: (a) mixing KH₂PO₄ and BaSO₄ in a weight ratio betweenabout 2:1 and about 1:8, to produce a precursor catalyst, (b) heatingsaid precursor catalyst between about 200° C. and about 650° C. forabout 1 hour to about 12 hours to produce a calcined precursor catalyst,(c) optionally grinding and sieving said calcined precursor catalyst toproduce a ground calcined precursor catalyst, and (d) contacting saidcalcined precursor catalyst or said ground calcined precursor catalystwith a gas feed stream comprising nitrogen and water vapor; wherein thewater partial pressure in said gas feed stream is between about 5 barand about 15 bar; and wherein said contacting is performed at atemperature between about 325° C. and about 425° C. to produce saidactive catalyst.

In another embodiment of the present invention, the active catalyst isprepared via (a) mixing K₂HPO₄, (NH₄)₂HPO₄, and amorphous silica in aweight ratio between about 1.3:1.0:16.1 and about 1.3:1.0:1.2 to producea precursor catalyst, (b) heating said precursor catalyst between about200° C. and about 650° C. for about 1 hour to about 12 hours to producea calcined precursor catalyst, (c) optionally grinding and sieving saidcalcined precursor catalyst to produce a ground precursor catalyst, and(d) contacting said calcined precursor catalyst or said ground calcinedprecursor catalyst with a gas feed stream comprising nitrogen and watervapor; wherein the water partial pressure in said gas feed stream isbetween about 5 bar and about 15 bar and wherein said contacting isperformed at a temperature between about 325° C. and about 425° C. toproduce said active catalyst.

The method of preparing the precursor catalyst can comprise mixing oftwo or more different components. This mixing step can be performed byany method known to those skilled in the art, such as, by way of exampleand not limitation: solid mixing, impregnation, or co-precipitation. Inthe solid mixing method, the various components are physically mixedtogether with optional grinding using any method known to those skilledin the art, such as, by way of example and not limitation, shear,extensional, kneading, extrusion, ball milling, and others, andalternatively followed by any additional treatment or activation step.In the impregnation method, a suspension of an insoluble component (e.g.inert support) is treated with a solution of precursor catalyst solubleingredients, and the resulting material is then treated or activatedunder conditions that will convert the mixture to a more active orpreferred state. In the co-precipitation method, a homogeneous solutionof the precursor catalyst ingredients is precipitated by the addition ofadditional ingredients, followed by optional filtration and heating toremove solvents and volatile materials (e.g., water, nitric acid, carbondioxide, ammonia, or acetic acid).

Mixing of precursor catalyst components with surfactants followed byheating can increase the precursor catalyst surface area. In oneembodiment of the present invention, the method of preparing thecatalyst further comprises mixing one or more surfactants with saidprecursor catalyst before said contacting with said gas feed stream. Inanother embodiment of the present invention, said one or moresurfactants are cationic or zwitterionic. Non-limiting examples ofsurfactants are myristyltrimethylammonium bromide,hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide,decyltrimethylammonium bromide, and octadecyltrimethyl ammonium bromide.

Heating can promote chemical reactions, thermal decompositions, phasetransitions, and/or removal of volatile materials. In one embodiment ofthe present invention, the method of preparing the active catalystfurther comprises heating said precursor catalyst at a temperature equalto or greater than 180° C. before said contacting with said gas feedstream. In another embodiment of the present invention, the method ofpreparing the active catalyst further comprises heating said precursorcatalyst at a temperature equal to or greater than 300° C. before saidcontacting with said gas feed stream. In yet another embodiment of thepresent invention, the method of preparing the active catalyst furthercomprises heating said precursor catalyst at a temperature between about350° C. and about 650° C. before said contacting with said gas feedstream. In even yet another embodiment of the present invention, themethod of preparing the active catalyst further comprises heating saidprecursor catalyst at a temperature between about 400° C. and about 450°C. before said contacting with said gas feed stream. Said heating istypically done using any method known to those skilled in the art, suchas, by way of example and not limitation, convection, conduction,radiation, microwave heating, and others. The heating is performed withequipment such as, by way of example and not limitation, furnaces,atomizers, or reactors of various designs, comprising shaft furnaces,rotary kilns, hearth furnaces, fluidized bed reactors, spay dryers. Theduration of said heating is, in one embodiment of the present invention,between about 1 hour and about 72 hours. In another embodiment, theduration of said heating is between about 2 hours and about 12 hours. Inyet another embodiment, the duration of said heating is about 4 hours.In one embodiment, the temperature ramp in said heating is between about0.5° C./min and about 20° C./min. In another embodiment, the temperatureramp in said heating is about 10° C./min.

V Methods of Making Acrylic Acid, Acrylic Acid Derivatives, or MixturesThereof

A method of dehydrating hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof to acrylic acid, acrylic acidderivatives, or mixtures thereof is provided. In one embodiment of thepresent invention, said hydroxypropionic acid is selected from the groupconsisting of lactic acid (2-hydroxypropionic acid), 3-hydroxypropionicacid, and mixtures thereof; and said hydroxypropionic acid derivativesare selected from the group consisting of lactic acid derivatives,3-hydroxypropionic acid derivatives, and mixtures thereof.

In another embodiment of the present invention, said hydroxypropionicacid is lactic acid and said hydroxypropionic acid derivatives arelactic acid derivatives. Lactic acid can be D-lactic acid, L-lacticacid, or mixtures thereof (including racemic mixture). Lactic acidderivatives can be metal or ammonium salts of lactic acid, alkyl estersof lactic acid, lactic acid oligomers, cyclic di-esters of lactic acid,lactic acid anhydride, 2-alkoxypropionic acids or their alkyl esters,2-aryloxypropionic acids or their alkyl esters, 2-acyloxypropionic acidsor their alkyl esters, or a mixture thereof. Non-limiting examples ofmetal salts of lactic acid are sodium lactate, potassium lactate, andcalcium lactate. Non-limiting examples of alkyl esters of lactic acidare methyl lactate, ethyl lactate, butyl lactate, 2-ethylhexyl lactate,and mixtures thereof. A non-limiting example of cyclic di-esters oflactic acid is dilactide. Non-limiting examples of 2-alkoxypropionicacids are 2-methoxypropionic acid and 2-ethoxypropionic acid. Anon-limiting example of 2-aryloxypropionic acid is 2-phenoxypropionicacid. A non-limiting example of 2-acyloxypropionic acid is2-acetoxypropionic acid. In yet another embodiment of the presentinvention, the lactic acid derivative is methyl lactate. Methyl lactatecan be neat or in a solution with water, methanol, or mixtures thereof.3-hydroxypropionic acid derivatives can be metal or ammonium salts of3-hydroxypropionic acid, alkyl esters of 3-hydroxypropionic acid,3-hydroxypropionic acid oligomers, 3-alkoxypropionic acids or theiralkyl esters, 3-aryloxypropionic acids or their alkyl esters,3-acyloxypropionic acids or their alkyl esters, or a mixture thereof.Non-limiting examples of metal salts of 3-hydroxypropionic acid aresodium 3-hydroxypropionate, potassium 3-hydroxypropionate, and calcium3-hydroxypropionate. Non-limiting examples of alkyl esters ofhydroxypropionic acid are methyl 3-hydroxypropionate, ethyl3-hydroxypropionate, butyl 3-hydroxypropionate, 2-ethylhexyl3-hydroxypropionate, and mixtures thereof. Non-limiting examples of3-alkoxypropionic acids are 3-methoxypropionic acid and3-ethoxypropionic acid. A non-limiting example of 3-aryloxypropionicacid is 3-phenoxypropionic acid. A non-limiting example of3-acyloxypropionic acid is 3-acetoxypropionic acid.

Hydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof can be produced by sugar fermentation or chemical conversion ofsugars or other feedstock materials, such as glycerin. Nearly all worldproduction of lactic acid is by sugar fermentation today; however, thereare chemical conversion technologies currently in pilot or demo scale.Also, the sugar feedstock can be generation 1 sugar (i.e., sugar fromcorn, sugarcane, sugar beets, wheat, potato, rice, etc.) or generation 2sugar (i.e., sugar from the hydrolysis of biomass or agricultural waste,such as bagasse, corn stover, rice husk, wheat straw, etc.).

Acrylic acid derivatives can be metal or ammonium salts of acrylic acid,alkyl esters of acrylic acid, acrylic acid oligomers, or mixturesthereof. Non-limiting examples of metal salts of acrylic acid are sodiumacrylate, potassium acrylate, and calcium acrylate. Non-limitingexamples of alkyl esters of acrylic acid are methyl acrylate, ethylacrylate, butyl acrylate, 2-ethylhexyl acrylate, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprises contactinga gas feed stream comprising water vapor and hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof with any activecatalyst disclosed in Section II (“Active Catalysts for the Dehydrationof Hydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any precursor catalyst disclosed in Section III(“Precursor Catalysts for the Dehydration of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) of the presentinvention in a reactor at a temperature, a water partial pressure, aGHSV, and a WHSV to dehydrate said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof, whereby acrylicacid, acrylic acid derivatives, or mixtures thereof are produced as aresult of the dehydration in the reactor.

In one embodiment of the present invention, said gas feed streamcomprises water vapor and hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof. In another embodiment of the presentinvention, said gas feed stream further comprises an essentiallychemically inert gas (also called herein diluent). In the context of thepresent invention, an essentially chemically inert gas is any gas thatis essentially chemically inert to said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof, but notnecessarily to said catalyst. Non-limiting examples of essentiallychemically inert gases or diluents are nitrogen, helium, argon, carbondioxide, carbon monoxide, and mixtures thereof. In yet anotherembodiment of the present invention, said essentially chemically inertgas or diluent comprises nitrogen. In even yet another embodiment of thepresent invention, said essentially chemically inert gas or diluentconsists essentially of nitrogen. In one embodiment of the presentinvention, said gas feed stream further comprises a gas selected fromthe group consisting of air and oxygen.

In one embodiment of the present invention, the concentration of thehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said gas feed stream is between about 0.5 mol % and about 95mol % (under STP conditions). In another embodiment of the presentinvention, the concentration of the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof in said gas feedstream is between about 1.5 mol % and about 20 mol % (under STPconditions). In yet another embodiment of the present invention, theconcentration of the hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof in said gas feed stream is betweenabout 2 mol % and about 5 mol % (under STP conditions). In even yetanother embodiment of the present invention, the concentration of thehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said gas feed stream is about 2.5 mol % (under STPconditions). In one embodiment of the present invention, theconcentration of the hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof in said gas feed stream is about 2.5mol % (under STP conditions), the concentration of the water vapor insaid gas feed stream is about 50 mol % (under STP conditions), and theconcentration of nitrogen in said gas feed stream is about 47.5 mol %(under STP conditions). In another embodiment of the present invention,the concentration of the hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof in said gas feed stream is about 10 mol% (under STP conditions) and the concentration of the water vapor insaid gas feed stream is about 90 mol % (under STP conditions).

In one embodiment of the present invention, the concentration of thelactic acid, lactic acid derivatives, or mixtures thereof in said gasfeed stream is between about 0.5 mol % and about 95 mol %. In anotherembodiment of the present invention, the concentration of the lacticacid, lactic acid derivatives, or mixtures thereof in said gas feedstream is between about 1.5 mol % and about 20 mol %. In yet anotherembodiment of the present invention, the concentration of the lacticacid, lactic acid derivatives, or mixtures thereof in said gas feedstream is between about 2 mol % and about 5 mol %. In even yet anotherembodiment of the present invention, the concentration of the lacticacid, lactic acid derivatives, or mixtures thereof in said gas feedstream is about 2.5 mol %. In one embodiment of the present invention,the concentration of the lactic acid, lactic acid derivatives, ormixtures thereof in said gas feed stream is about 2.5 mol %, theconcentration of the water vapor in said gas feed stream is about 50 mol%, and the concentration of nitrogen in said gas feed stream is about47.5 mol %. In another embodiment of the present invention, theconcentration of the lactic acid, lactic acid derivatives, or mixturesthereof in said gas feed stream is about 10 mol % and the concentrationof the water vapor in said gas feed stream is about 90 mol %.

Non-limiting examples of reactors suitable for use in the presentinvention are static reactors, stirred tank reactors, recirculationreactors, fluidized bed reactors, packed-bed flow reactors, andcombinations thereof. In one embodiment of the present invention, thegas feed stream flows down the reactor. In another embodiment of thepresent invention, the gas feed stream flows up the reactor. In yetanother embodiment of the present invention, the gas feed stream flowshorizontally in the reactor.

In one embodiment of the present invention, the reactor is a packed-bedflow reactor. Typically, a packed-bed flow reactor is a tubular reactor.In another embodiment of the present invention, the tubular packed-bedflow reactor is a single-layer reactor. In yet another embodiment of thepresent invention, the tubular packed-bed flow reactor is a bi-layerreactor. A half cross section of an exemplary tubular single-layerreactor is shown in FIG. 2, and a half cross section of an exemplarytubular bi-layer reactor is shown in FIG. 3.

In FIG. 2, a single-layer reactor 3 consists of a single layer 25 (alsocalled wall) that extends from an inner surface 35 to an outer surface55 and has a wall thickness. The inner surface 35 is in contact with acatalyst 65. In one embodiment of the present invention, thesingle-layer reactor comprises a wall, an outer surface, and an innersurface; wherein said wall is made from a wall material, has a wallthickness, and extends from said outer surface to said inner surface;and wherein said inner surface is in contact with said catalyst. Inanother embodiment of the present invention, the wall thickness of asingle-layer reactor is in accordance to the Nominal Pipe Standard (NPS)for seamless and welded steel pipes (ANSI B36.10 of 1979). In yetanother embodiment of the present invention, the wall thickness of asingle-layer reactor is between about 0.65 in. (1.651 mm) and about 0.5in. (12.7 mm). In even yet another embodiment of the present invention,the wall thickness of a single-layer reactor is between about 0.65 in.(1.651 mm) and about 0.432 in. (10.973 mm). In one embodiment of thepresent invention, the wall thickness of a single-layer reactor isbetween about 0.065 in. (1.651 mm) and about 0.337 in. (8.56 mm). Inanother embodiment of the present invention, the wall thickness of asingle-layer reactor is about 0.133 in. (3.378 mm).

In FIG. 3, a bi-layer reactor 5 comprises an inner surface 30 that comesin contact with a catalyst 60 and is the innermost surface of thebi-layer reactor 5. The bi-layer reactor 5 consists of an inner layer10, which has an inner layer thickness, an outer layer 20, which has anouter layer thickness, an interface 40 between the outer layer 20 andthe inner layer 10, and an outer surface 50, which is the outmostsurface of the tubular reactor 5. In one embodiment of the presentinvention, the outer layer 20 of the bi-layer reactor 5 consists of twoor more sublayers. In another embodiment of the present invention, thebi-layer reactor comprises an outer layer, an inner layer, an outersurface, an inner surface, and an interface between said outer layer andsaid inner layer; wherein said outer layer is made from an outer layermaterial, has an outer layer thickness, and extends from said interfaceto said outer surface; wherein said inner layer is made from an innerlayer material, has an inner layer thickness, and extends from saidinner surface to said interface; and wherein said inner surface is incontact with said catalyst. In yet another embodiment of the presentinvention, said outer layer comprises two or more sublayers.

In one embodiment of the present invention, the inner layer thickness ofa bi-layer reactor is between about 1 mm and about 20 mm. In anotherembodiment of the present invention, the inner layer thickness of abi-layer reactor is between about 1.5 mm and about 10 mm. In yet anotherembodiment of the present invention, the inner layer thickness of abi-layer reactor is between about 2 mm and about 8 mm. In even yetanother embodiment of the present invention, the inner layer thicknessof a bi-layer reactor is between about 3 mm and about 6 mm.

In one embodiment of the present invention, the outer layer thickness ofa bi-layer reactor is between about 1 mm and about 20 mm. In anotherembodiment of the present invention, the outer layer thickness of abi-layer reactor is between about 1.6 mm and about 12.7 mm. In yetanother embodiment of the present invention, the outer layer thicknessof a bi-layer reactor is between about 2 mm and about 9 mm. In even yetanother embodiment of the present invention, the outer layer thicknessof a bi-layer reactor is between about 3 mm and about 6 mm.

In one embodiment of the present invention, the outer diameter (OD) of asingle-layer or a bi-layer reactor is in accordance to the Nominal PipeStandard (NPS) for seamless and welded steel pipes (ANSI B36.10 of1979). In another embodiment of the present invention, the OD of asingle-layer or bi-layer reactor is between about 0.84 in. (21.34 mm)and about 9.625 in. (244.48 mm). In yet another embodiment of thepresent invention, the OD of a single-layer or a bi-layer reactor isbetween about 1.315 in. (33.4 mm) and about 6.625 in. (168.28 mm). Ineven yet another embodiment of the present invention, the OD of asingle-layer or a bi-layer reactor is between about 2.375 in. (60.33 mm)and about 4.5 in. (114.3 mm). In one embodiment of the presentinvention, the OD of a single-layer or a bi-layer reactor is about 1.315in. (33.4 mm).

The inner layer of a bi-layer reactor can be formed by a variety ofmethods. Non-limiting examples of methods to form the inner layer of abi-layer reactor are bonding of the inner layer to the outer layer anddipping of the outer layer in a bath comprising the inner layermaterial. In one embodiment of the preset invention, the inner layer isformed by a bonding process of the inner layer to the outer layer. Inanother embodiment of the present invention, the bonding process isselected from the group consisting of cladding, laser cladding,explosion cladding, electromagnetic fusion cladding, fusion welding,explosion welding, gluing, pressing, rolling, coextrusion, thermalspraying, electroplating, and chemical vapor deposition. Non-limitingexamples of bonding processes are cladding of a copper tube (innerlayer) inside a stainless steel outer layer, explosion cladding of azirconium tube (inner layer) inside a stainless steel outer layer, andelectroplating silver on a stainless steel outer layer. In yet anotherembodiment of the present invention, the inner layer is bonded to theouter layer in the form of flat sheets, which are then welded into areactor tube with an inner layer and an outer layer.

In yet another embodiment of the present invention, the inner layer isformed by a dipping process of the outer layer in a bath comprising theinner layer material. Non-limiting examples of stainless steel outerlayer materials and aluminum or aluminum and silicon mixture inner layermaterials that have been formed via a dipping process are the followingcommercial alloys: Aluminized Steel Type 1 Stainless 409 and AluminizedSteel Type 1 Stainless 439 (the inner layer material is a mixture ofaluminum and silicon); and Aluminized Steel Type 2 (the inner layermaterial is aluminum only); all from AK Steel Corp. (West Chester,Ohio). The dipping process can be operated in batch, continuous, orsemi-continuous modes.

The active catalysts of the present invention can be corrosive to thereactors because they are amorphous and partially-dehydrated phosphatesalts. Unexpectedly, it has been found that some specific metals in theinner layer material of bi-layer reactors or wall material ofsingle-layer reactors can reduce or eliminate the corrosive effects ofthe active catalysts, i.e., these metals are corrosion resistant reactormetals. Not wishing to be bound by any theory, applicants believe thatthe corrosion resistant reactor metals either: 1) form oxides and a thinpassivating layer containing these oxides on the inner surface of thereactors (i.e., the surface of the reactor that is in contact with thecatalyst and gas feed stream); or 2) have corrosion immunity as metalsunder the dehydration conditions. The oxide-based surface passivatinglayer can form when the inner surface of the reactor is subjected tooxidation. In one embodiment of the present invention, the oxidationoccurs during the dehydration. In another embodiment of the presentinvention, the oxidation occurs before the dehydration. In yet anotherembodiment of the present invention, the oxidation that occurs beforethe dehydration can be a result of a pre-treatment step of the reactor.In either case, the oxide-based surface passivating layer reduces oreliminates the oxidation of other reactor metals and migration of theresulting ions into the catalyst bed (i.e., corrosion). Migration of themetal ions into the catalyst particles can have detrimental effects onthe yield and selectivity of the produced acrylic acid, acrylic acidderivatives, or mixtures thereof, and catalyst lifetime, besideslowering the reactor strength itself. The metal cation in the oxide canbe a metal in the inner layer material or wall material.

In one embodiment of the present invention, the bonding process isfollowed by oxidation of the inner surface. In another embodiment of thepresent invention, the dipping process is followed by oxidation of theinner surface.

A non-limiting example of a metal that forms an oxide-based surfacepassivating layer is aluminum contained in significant amounts (e.g.greater than about 1 wt %) in various inner layer or wall materials whenthe reactor is oxidized before or during the dehydration reaction. Inone embodiment of the present invention, the inner surface is subjectedto oxidation and forms an oxide-based surface passivating layercomprising alumina. Non-limiting examples of wall materials that havehigh aluminum content and form an oxide-based surface passivating layerof alumina on the inner surface of the reactor are the followingcommercial alloys: KANTHAL APM (ferritic iron-chromium-aluminum alloy;FeCrAl alloy) and KANTHAL APMT (ferriticiron-chromium-aluminum-molybdenum alloy; FeCrAlMo alloy) from Sandvik AB(Stockholm, Sweden); HAYNES® 214® and HAYNES® HR-224® alloys (both areNi-based alloys) from Haynes International, Inc. (Kokomo, Ind.);INCONEL® alloy 693 and INCONEL® alloy 601 (both are Ni-based alloys),and INCOLLOY® alloy MA956 (Fe—Cr—Al alloy) from Special MetalsCorporation (Huntington, W. Va.); and Fercalloy, Fercalloy 145,Fercalloy 135, and Resistalloy 134 from Resistalloy Trading Limited(Sheffield, South Yorkshire, UK).

A non-limiting example of a metal that forms an oxide-based surfacepassivating layer is silicon contained in significant amounts (e.g.greater than about 1 wt %) in various inner layer or wall materials whenthe reactor is oxidized before or during the dehydration reaction. Inone embodiment of the present invention, the inner surface is subjectedto oxidation and forms an oxide-based surface passivating layercomprising silica. Non-limiting examples of wall materials that havehigh silicon content and form an oxide-based surface passivating layerof silica on the inner surface of the reactor are the followingcommercial alloys: Sandvik SX and Sandvik 253 MA (both are austeniticsteel alloys) from Sandvik AB (Stockholm, Sweden); and HAYNES® HR-160®and HASTELLOY® D-205 alloys (both are Ni-based alloys) from HaynesInternational, Inc. (Kokomo, Ind.). For the purposes of the presentinvention, Ni-based alloys are alloys that contain Ni in an amountgreater than about 35 wt %.

A non-limiting example of a metal mixture that is the inner layermaterial of a bi-layer reactor is a mixture of aluminum and silicon thatis formed as the inner layer via a dipping process when a stainlesssteel outer layer is dipped into a hot bath comprising aluminum andsilicon and forms the aluminum and silicon inner layer. Then, thesurface of the inner layer is oxidized either before or during thedehydration reaction to form an oxide-based surface passivating layer onthe inner surface of the reactor comprising alumina and silica. In oneembodiment of the present invention, the inner surface is subjected tooxidation and forms an oxide-based surface passivating layer comprisingalumina and silica.

Typically, the thickness of the oxide-based surface passivating layer isbetween about 0.1 nm and 1 μm. In one embodiment of the presentinvention, the thickness of the oxide-based surface passivating layer isbetween about 0.3 nm and about 100 nm. In another embodiment of thepresent invention, the thickness of the oxide-based surface passivatinglayer is between about 1 nm and about 50 nm. In yet another embodimentof the present invention, the thickness of the oxide-based surfacepassivating layer is between about 5 nm and about 25 nm.

The inner layer, after it is formed by either a bonding process or adipping process, can be subjected to oxidation to form an oxide-basedsurface passivating layer on the inner surface. The oxidation processcan occur before the dehydration process or during the dehydrationprocess, since the gas feed stream comprises water vapor. The oxidationprocess conditions depend on the inner layer material and are typicallywell known to those skilled in the art. Non-limiting examples of theoxidation process before the dehydration involve the use of air oroxygen atmospheres and: 1) temperature greater than about 500° C. andduration of a few hours, or 2) a 2-step process, where in step 1 thetemperature is about 600° C. and the duration is about 1 hour, and instep 2 the temperature is about 1,000° C. and the duration is about 1hour.

In one embodiment of the present invention, the inner layer material isselected from the group consisting of aluminum, silicon, copper, silver,gold, titanium, tantalum, tungsten, molybdenum, platinum, palladium,zirconium, or mixtures thereof. From the group of metals disclosedabove, aluminum, silicon, titanium, tantalum, tungsten, molybdenum, andzirconium reduce or eliminate the corrosive effects of the activecatalysts by forming oxides and oxide-based surface passivating layers;whereas, copper, silver, gold, platinum, and palladium reduce oreliminate the corrosive effects of the active catalysts as metals (notoxides) because of their corrosion immunity. In another embodiment ofthe present invention, the reactor material composition comprises ametal selected from the group consisting of aluminum, silicon, andmixtures thereof. In another embodiment of the present invention, theinner layer material is selected from the group consisting of copper,silver, and gold. In yet another embodiment of the present invention,the inner layer material is selected from the group consisting oftitanium, tantalum, tungsten, molybdenum, platinum, palladium,zirconium, and mixtures thereof. In even yet another embodiment of thepresent invention, the inner layer material is selected from the groupconsisting of aluminum, silicon, copper, silver, and mixtures thereof.In one embodiment of the present invention, the inner layer material iscopper. In another embodiment of the present invention, the inner layermaterial is silver. In another embodiment of the present invention, theinner layer material is zirconium. In yet another embodiment of thepresent invention, the inner layer material is titanium.

In one embodiment of the present invention, the bonding process isfollowed by oxidation of the inner surface when the inner layer materialis selected from the group consisting of aluminum, silicon, titanium,tantalum, tungsten, molybdenum, zirconium, and mixtures thereof. Inanother embodiment of the present invention, the dipping process isfollowed by oxidation of the inner surface when the inner layer materialis selected from the group consisting of aluminum, silicon, titanium,tantalum, tungsten, molybdenum, zirconium, and mixtures thereof.

In one embodiment of the present invention, the outer layer material isselected from the group consisting of carbon steel, stainless steel,titanium, Ni-based alloy, and mixtures thereof. In another embodiment ofthe present invention, the outer layer material is Ni-based alloy. Inyet another embodiment of the present invention, the outer layermaterial is selected from the group consisting of stainless steel andcarbon steel. In even yet another embodiment of the present invention,the outer layer material is carbon steel. In one embodiment of thepresent invention, the outer layer material is stainless steel.

In one embodiment of the present invention, the outer layer material isstainless steel and the inner layer material of the bi-layer reactor isselected from the group consisting of aluminum, silicon, and mixturesthereof. In another embodiment of the present invention, the outer layermaterial is stainless steel and the inner layer material of the bi-layerreactor is aluminum. In yet another embodiment of the present invention,the outer layer material is carbon steel and the inner layer material ofthe bi-layer reactor is selected from the group consisting of aluminum,silicon, and mixtures thereof. In even yet another embodiment of thepresent invention, the outer layer material is carbon steel and theinner layer material of the bi-layer reactor is aluminum.

Non-limiting examples of stainless steels are ferritic stainless steels,martensitic stainless steels, austenitic stainless steels, and duplexstainless steels. All stainless steels contain at least 10.5 wt %chromium. Ferritic stainless steels are classified in the 400 series,contain very little nickel, and their common grades include 409, 439,18Cr-2Mo, 26Cr-1Mo, 29Cr-4Mo, and 29Cr-4Mo-2Ni. Martensitic stainlesssteels are classified in the 400 series, have higher levels of carbonthan the ferritic grades, and their common grades include 410 and 420.Austenitic stainless steel grades are classified in the 200 and 300series, make up over 70% of the stainless steel production, contain aminimum of 16 wt % chromium and 2 wt % to 20 wt % nickel, and their mostcommon grades are 201, 301, 304, 316, and 316 L. Finally, the duplexstainless steels have a mixed microstructure of austenitic and ferriticstainless steels, and have 19 wt % to 32 wt % chromium, up to 5 wt %molybdenum, and lower nickel contents than austenitic stainless steels.Sandvik AB (Stockholm, Sweden), Outokumpu Group (Espoo, Finland),ThyssenKrupp AG (Essen, Germany), Acerinox S.A. (Madrid, Spain), and AKSteel Corp. (West Chester, Ohio) are the main producers of stainlesssteel grades.

In one embodiment of the present invention, the outer layer material isstainless steel and the inner layer material of the bi-layer reactor iscopper. In another embodiment of the present invention, the outer layermaterial is stainless steel and the inner layer material of the bi-layerreactor is silver. In yet another embodiment of the present invention,the outer layer material is stainless steel and the inner layer materialof the bi-layer reactor is titanium. In even yet another embodiment ofthe present invention, the outer layer material is stainless steel andthe inner layer material of the bi-layer reactor is zirconium.

In one embodiment of the present invention, the outer layer material iscarbon steel and the inner layer material of the bi-layer reactor iscopper. Carbon steel contains carbon in the range of 0.12 wt % to 2 wt%, copper in the range of 0.4 wt % to 0.6 wt %, manganese at no morethan 1.65 wt %, and silicon at no more than 0.6 wt %. In anotherembodiment of the present invention, the outer layer material is carbonsteel and the inner layer material of the bi-layer reactor is silver. Inyet another embodiment of the present invention, the outer layermaterial is carbon steel and the inner layer material of the bi-layerreactor is titanium. In even yet another embodiment of the presentinvention, the outer layer material is carbon steel and the inner layermaterial of the bi-layer reactor is zirconium.

In one embodiment of the present invention, the outer layer material isstainless steel, the inner layer material is formed by a dipping processof the outer layer material of a bi-layer reactor in a bath comprisingaluminum and silicon, and the inner surface of the bi-layer reactor issubjected to oxidation and forms an oxide-based surface passivatinglayer comprising alumina and silica. In another embodiment of thepresent invention, the outer layer material is stainless steel, theinner layer material is formed by a dipping process of the outer layermaterial of a bi-layer reactor in a bath comprising aluminum, and theinner surface of the bi-layer reactor is subjected to oxidation andforms an oxide-based surface passivating layer comprising alumina.

In one embodiment of the present invention, the corrosion resistantreactor metal is selected from the group consisting of aluminum,silicon, copper, silver, gold, titanium, tantalum, tungsten, molybdenum,platinum, palladium, zirconium, and mixtures thereof. In anotherembodiment of the present invention, the corrosion resistant reactormetal is selected from the group consisting of aluminum, silicon,titanium, tantalum, tungsten, molybdenum, zirconium, and mixturesthereof. In yet another embodiment of the present invention, thecorrosion resistant reactor metal is selected from the group consistingof copper, silver, gold, platinum, palladium, and mixtures thereof. Ineven yet another embodiment of the present invention, the corrosionresistant reactor metal is selected from the group consisting ofaluminum, silicon, and mixtures thereof. In one embodiment of thepresent invention, the corrosion resistant reactor metal is aluminum. Inanother embodiment of the present invention, the corrosion resistantreactor metal is silicon. In yet another embodiment of the presentinvention, the corrosion resistant reactor metal is selected from thegroup consisting of aluminum, silicon, and mixtures thereof. In even yetanother embodiment of the present invention, the corrosion resistantreactor metal is copper. In one embodiment of the present invention, thecorrosion resistant reactor metal is silver.

In one embodiment of the present invention, the corrosion resistantreactor metal is present in the reactor material in an amount greaterthan about 1 wt %. In another embodiment of the present invention, thecorrosion resistant reactor metal is present in the reactor material inan amount greater than about 2 wt %. In yet another embodiment of thepresent invention, the corrosion resistant reactor metal is present inthe reactor material in an amount greater than about 3 wt %. In even yetanother embodiment of the present invention, the corrosion resistantreactor metal is present in the reactor material in an amount greaterthan about 4 wt %. In one embodiment of the present invention, thecorrosion resistant reactor metal is present in the reactor material inan amount between about 1 wt % and about 6 wt %. In another embodimentof the present invention, the corrosion resistant reactor metal ispresent in the reactor material in an amount between about 3 wt % andabout 5 wt %.

In one embodiment of the present invention, the wall material comprisesaluminum in an amount greater than about 1 wt %. In another embodimentof the present invention, the wall material comprises aluminum in anamount greater than about 2 wt %. In yet another embodiment of thepresent invention, the wall material comprises aluminum in an amountgreater than about 3 wt %. In even yet another embodiment of the presentinvention, the wall material comprises aluminum in an amount greaterthan about 4 wt %. In one embodiment of the present invention, the wallmaterial comprises aluminum in an amount between about 1 wt % and about50 wt %. In another embodiment of the present invention, the wallmaterial comprises aluminum in an amount between about 1 wt % and about6 wt %. In yet another embodiment of the present invention, the wallmaterial comprises aluminum in an amount between about 1 wt % and about4 wt %. In even yet another embodiment of the present invention, thewall material comprises aluminum in an amount between about 3 wt % andabout 5 wt %.

In one embodiment of the present invention, the wall material comprisessilicon in an amount greater than about 1 wt %. In another embodiment ofthe present invention, the wall material comprises silicon in an amountgreater than about 2 wt %. In yet another embodiment of the presentinvention, the wall material comprises silicon in an amount greater thanabout 3 wt %. In even yet another embodiment of the present invention,the wall material comprises silicon in an amount greater than about 4 wt%. In one embodiment of the present invention, the wall materialcomprises silicon in an amount between about 1 wt % and about 50 wt %.In another embodiment of the present invention, the wall materialcomprises silicon in an amount between about 1 wt % and about 6 wt %. Inyet another embodiment of the present invention, the wall materialcomprises silicon in an amount between about 3 wt % and about 5 wt %.

In one embodiment of the present invention, the wall material furthercomprises nickel in an amount between about 50 wt % and about 75 wt %.In another embodiment of the present invention, the wall materialfurther comprises chromium in an amount between about 15 wt % and about20 wt %. In yet another embodiment of the present invention, the wallmaterial further comprises iron in an amount between about 3 wt % andabout 30 wt %. In even yet another embodiment of the present invention,the wall material further comprises nickel in an amount between about 50wt % and about 75 wt %, chromium in an amount between about 15 wt % andabout 20 wt %, and iron in an amount between about 3 wt % and about 30wt %. In one embodiment of the present invention, the wall materialcomprises aluminum in an amount greater than about 1 wt %, nickel in anamount between about 50 wt % and about 75 wt %, chromium in an amountbetween about 15 wt % and about 20 wt %, and iron in an amount betweenabout 3 wt % and about 30 wt %. Non-limiting examples of commercial wallmaterials with compositions within the above disclosure are HAYNES® 214®and HAYNES® HR-224® alloys from Haynes International, Inc. (Kokomo,Ind.).

In one embodiment of the present invention, the wall material furthercomprises nickel in an amount of about 60 wt %. In another embodiment ofthe present invention, the wall material further comprises chromium inan amount between about 20 wt % and about 30 wt %. In yet anotherembodiment of the present invention, the wall material further comprisesiron in an amount between about 3 wt % and about 20 wt %. In even yetanother embodiment of the present invention, the wall material furthercomprises nickel in an amount of about 60 wt %, chromium in an amountbetween about 20 wt % and about 30 wt %, and iron in an amount betweenabout 3 wt % and about 20 wt %. In one embodiment of the presentinvention, the wall material comprises aluminum in an amount greaterthan about 1 wt %, nickel in an amount of about 60 wt %, chromium in anamount between about 20 wt % and about 30 wt %, and iron in an amountbetween about 3 wt % and about 20 wt %. Non-limiting examples ofcommercial wall materials with compositions within the above disclosureare INCONEL® alloy 693 and INCONEL® alloy 601 from Special MetalsCorporation (Huntington, W. Va.).

In one embodiment of the present invention, the wall material furthercomprises iron in an amount of about 70 wt %. In another embodiment ofthe present invention, the wall material further comprises chromium inan amount of about 22 wt %. In yet another embodiment of the presentinvention, the wall material further comprises iron in an amount ofabout 70 wt % and chromium in an amount of about 22 wt %. In even yetanother embodiment of the present invention, the wall material comprisesaluminum in an amount greater than about 1 wt %, iron in an amount ofabout 70 wt %, and chromium in an amount of about 22 wt %. Non-limitingexamples of commercial wall materials with compositions within the abovedisclosure are KANTHAL APM and KANTHAL APMT from Sandvik AB (Stockholm,Sweden); and INCOLLOY® alloy MA956 (Fe—Cr—Al alloy) from Special MetalsCorporation (Huntington, W. Va.).

In one embodiment of the present invention, the wall material furthercomprises nickel in an amount between about 10 wt % and about 65 wt %.In another embodiment of the present invention, the wall materialfurther comprises chromium in an amount between about 15 wt % and about30 wt %. In yet another embodiment of the present invention, the wallmaterial further comprises iron in an amount between about 2 wt % andabout 65 wt %. In even yet another embodiment of the present invention,the wall material comprises silicon in an amount greater than about 1 wt%, nickel in an amount between about 10 wt % and about 65 wt %, chromiumin an amount between about 15 wt % and about 30 wt %, and iron in anamount between about 2 wt % and about 65 wt %. Non-limiting examples ofcommercial wall materials with compositions within the above disclosureare Sandvik SX and Sandvik 253 MA from Sandvik AB (Stockholm, Sweden),and HAYNES® HR-160® and HASTELLOY® D-205 alloys from HaynesInternational, Inc. (Kokomo, Ind.).

In one embodiment of the present invention, the single-layer reactor hasa corrosion rate lower than about 1.3 mm/y. In another embodiment of thepresent invention, the bi-layer reactor has a corrosion rate lower thanabout 1.3 mm/y. For the purposes of the present invention, the corrosionrate is measured using a metallographic technique as shown in FIG. 4(copied from a Haynes International, Inc., brochure). More specificallyin this technique (known to those skilled in the art), a test metalcoupon is embedded in the catalyst bed and the dehydration reactionproceeds for a period of TOS (in h). After the dehydration reactionstops, the metal coupon is removed from the catalyst bed and subjectedto a typical metallographic analysis, that includes mounting the samplein a thermosetting resin, curing the resin, grinding the sample toreveal its surface, and SEM analysis of the sample to calculate themetal loss [(A−B)/2] in mm, as shown in FIG. 4. Then, the corrosion rate(CR) in mm per year (mm/y) is calculated as CR={[(A−B)/2]*24*365}/TOS,where 24 refers to the hours per day and 365 refers to the days peryear. Note that this equation assumes that the corrosion observed overTOS (typically a few hours to about 72 hours) linearly extrapolates outto a year, which is not necessarily accurate.

In one embodiment of the present invention, said corrosion rate is lowerthan about 1 mm/y. In another embodiment of the present invention, saidcorrosion rate is lower than about 0.5 mm/y. In yet another embodimentof the present invention, said corrosion rate is lower than about 0.13mm/y. In even yet another embodiment of the present invention, saidcorrosion rate is lower than about 0.05 mm/y.

In one embodiment of the present invention, said corrosion resistantreactor metal has a standard free energy of formation of oxides greaterthan about 700 kJ/mol O₂ at about 400° C. The standard free energy offormation of oxides can be found in the Ellingham diagram, as it is wellknown to those skilled in the art. In another embodiment of the presentinvention, said corrosion resistant reactor metal has a standard freeenergy of formation of oxides greater than about 950 kJ/mol O₂ at about400° C. In yet another embodiment of the present invention, saidcorrosion resistant reactor metal has a standard free energy offormation of oxides greater than about 1050 kJ/mol O₂ at about 400° C.In even yet another embodiment of the present invention, said corrosionresistant reactor metal is selected from the group consisting of Ca, Mg,and mixtures thereof.

In one embodiment of the present invention, said corrosion resistantreactor metal has a voltage potential, with respect to the standardhydrogen electrode (SHE), less than about 0.2 V at about 25° C., pH lessthan about 7, and concentration of the oxidized species of about 10⁻⁶mol/kg in water. The voltage potential of the reactor metal can be foundin the Pourbaix diagram of the metal or it can be estimated using theNernst equation, as it is well known to those skilled in the art. Inanother embodiment of the present invention, said corrosion resistantreactor metal has a voltage potential, with respect to the standardhydrogen electrode (SHE), less than about 0 V at about 25° C., pH lessthan about 7, and concentration of the oxidized species of about 10⁻⁶mol/kg in water. In yet another embodiment of the present invention,said corrosion resistant reactor metal has a voltage potential, withrespect to the standard hydrogen electrode (SHE), between about 0.2 Vand about −0.3 V at about 25° C., pH less than about 7, andconcentration of the oxidized species of about 10⁻⁶ mol/kg in water.

In one embodiment of the present invention, the temperature during saiddehydration is greater than about 100° C. In another embodiment of thepresent invention, the temperature during said dehydration is betweenabout 120° C. and about 700° C. In yet another embodiment of the presentinvention, the temperature during said dehydration is between about 150°C. and about 500° C. In even yet another embodiment of the presentinvention, the temperature during said dehydration is between about 300°C. and about 450° C. In one embodiment of the present invention, thetemperature during said dehydration is between about 325° C. and about400° C. In another embodiment of the present invention, the temperatureduring said dehydration is about 350° C. In yet another embodiment ofthe present invention, the temperature during said dehydration is about375° C. In even yet another embodiment of the present invention, thetemperature during said dehydration is equal to or greater than thetriple point temperature of said catalyst. In one embodiment of thepresent invention, the temperature during said dehydration is at least10° C. higher than the triple point temperature of said catalyst. Inanother embodiment of the present invention, the temperature during saiddehydration is at least 50° C. higher than the triple point temperatureof said catalyst. In yet another embodiment of the present invention,the temperature during said dehydration is at least 100° C. higher thanthe triple point temperature of said catalyst.

In one embodiment of the present invention, said water partial pressureduring said dehydration is equal to or greater than about 0.4 bar. Inanother embodiment of the present invention, said water partial pressureduring said dehydration is equal to or greater than about 0.8 bar. Inyet another embodiment of the present invention, said water partialpressure during said dehydration is equal to or greater than about 4bar. In even yet another embodiment of the present invention, said waterpartial pressure during said dehydration is between about 5 bar andabout 35 bar. In one embodiment of the present invention, said waterpartial pressure during said dehydration is about 13 bar. In oneembodiment of the present invention, the water partial pressure duringsaid dehydration is equal to or greater than the triple point waterpartial pressure of said catalyst. In another embodiment of the presentinvention, the water partial pressure during said dehydration is atleast 1 bar greater than the triple point water partial pressure of saidcatalyst. In yet another embodiment of the present invention, the waterpartial pressure during said dehydration is at least 2 bar greater thanthe triple point water partial pressure of said catalyst. In even yetanother embodiment of the present invention, the water partial pressureduring said dehydration is at least 5 bar greater than the triple pointwater partial pressure of said catalyst.

The dehydration can be performed under vacuum, at atmospheric pressure,or at higher pressure than atmospheric. In one embodiment of the presentinvention, the dehydration is performed under a total pressure of atleast about 1 bar. In another embodiment of the present invention, thedehydration is performed under a total pressure between about 2 bar andabout 100 bar. In yet another embodiment of the present invention, thedehydration is performed under a total pressure between about 5 bar andabout 40 bar. In even yet another embodiment of the present invention,the dehydration is performed under a total pressure between about 10 barand about 35 bar. In one embodiment of the present invention, thedehydration is performed under a total pressure of about 1.6 bar. Inanother embodiment of the present invention, the dehydration isperformed under a total pressure of about 8 bar. In yet anotherembodiment of the present invention, the dehydration is performed undera total pressure of about 26 bar.

In one embodiment of the present invention, said GHSV in the dehydrationis between about 720 h⁻¹ and about 36,000 h⁻¹. In another embodiment ofthe present invention, said GHSV is between about 1,440 h⁻¹ and about18,000 h⁻¹. In yet another embodiment of the present invention, saidGHSV is between about 2,300 h⁻¹ and about 6,000 h⁻¹. In even yet anotherembodiment of the present invention, said GHSV is between about 2,300h⁻¹ and about 3,600 h⁻¹. In one embodiment of the present invention,said GHSV is about 2,300 h⁻¹. In another embodiment of the presentinvention, said GHSV is about 3,600 h⁻¹.

In one embodiment of the present invention, said WHSV is between about0.02 h⁻¹ and about 10 h⁻¹. In another embodiment of the presentinvention, said WHSV is between about 0.2 h⁻¹ and about 2 h⁻¹. In yetanother embodiment of the present invention, said WHSV is between about0.3 h⁻¹ and about 1.4 h⁻¹. In even yet another embodiment of the presentinvention, said WHSV is between about 0.3 h⁻¹ and about 0.4 h⁻¹. In oneembodiment of the present invention, said WHSV is about 0.4 h⁻¹.

In the context of the present invention, “contacting” refers to theaction of bringing said gas feed stream comprising water vapor andhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in close proximity to the surface of said catalyst. Thehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof must contact the surface of the catalyst at a rate that is slowenough for the dehydration reaction to occur, yet fast enough to avoidthe degradation of hydroxypropionic acid, acrylic acid, or theirderivatives to undesirable products at the temperature of saidcontacting step. Several parameters can be used to describe the rate ofsaid contacting step, such as, by way of example and not limitation,WHSV, GHSV, LHSV, and weight velocity per unit of accessible catalystsurface area (WVSA) that can be calculated as the ratio of WHSV and thecatalyst specific surface area (SA), (WVSA=WHSV/SA); with units: g/m²·h;where g refer to g of hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof. A number of methods, based on theadsorption of an inert gas, can be used to determine the accessiblesurface area, including, but not limited to, the static volumetric andgravimetric methods and the dynamic method that are well-known by thoseskilled in the art.

In one embodiment of the present invention, the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof contact thecatalyst at a WVSA between about 10⁻⁴ g·m⁻²·h⁻¹ and about 10⁴ g·m⁻²·h⁻¹.In another embodiment of the present invention, the hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof contact thecatalyst at a WVSA between about 10⁻² g·m⁻²·h⁻¹ and about 10² g·m⁻²·h⁻¹.In yet another embodiment of the present invention, the hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof contact thecatalyst at a WVSA between about 0.1 g·m⁻²·h⁻¹ and about 10 g·m⁻²·h⁻¹.

In one embodiment of the present invention, said hydroxypropionic acidis lactic acid; wherein said gas feed stream comprises a diluent;wherein said diluent consists essentially of nitrogen; wherein saidtemperature is between about 300° C. and about 450° C.; wherein saidwater partial pressure is equal to or greater than 0.8 bar; and whereinsaid GHSV is between about 2,300 h⁻¹ and about 3,600 h⁻¹, and said WHSVis between about 0.2 h⁻¹ and about 2 h⁻¹.

In one embodiment of the present invention, the TOS is longer than about2 h. In another embodiment of the present invention, the TOS is betweenabout 2 h and about 24 h. In yet another embodiment of the presentinvention, the TOS is between about 24 h and about 48 h. In even yetanother embodiment of the present invention, the TOS is between about 24h and about 72 h. In one embodiment of the present invention, the TOS isabout 72 h. In another embodiment of the present invention, the TOS islonger than about 1000 h. In yet another embodiment of the presentinvention, the TOS is about 1 year.

In one embodiment of the present invention, said acrylic acid, acrylicacid derivatives, or mixtures thereof are produced with a yield of atleast 50 mol %. In another embodiment of the present invention, saidacrylic acid, acrylic acid derivatives, or mixtures thereof are producedwith a yield of at least about 70%. In yet another embodiment of thepresent invention, said acrylic acid, acrylic acid derivatives, ormixtures thereof are produced with a yield of at least about 80 mol %.

In one embodiment of the present invention, said acrylic acid, acrylicacid derivatives, or mixtures thereof are produced with a selectivity ofat least about 50 mol %. In another embodiment of the present invention,said acrylic acid, acrylic acid derivatives, or mixtures thereof areproduced with a selectivity of at least about 70 mol %. In yet anotherembodiment of the present invention, said acrylic acid, acrylic acidderivatives, or mixtures thereof are produced with a selectivity of atleast about 80 mol %.

In one embodiment of the present invention, said acrylic acid, acrylicacid derivatives, or mixtures thereof are produced with a yield of atleast about 70 mol % and with a selectivity of at least about 70 mol %.In another embodiment of the present invention, said acrylic acid,acrylic acid derivatives, or mixtures thereof are produced with a yieldof at least about 80 mol % and with a selectivity of at least about 80mol %.

In one embodiment of the present invention, propionic acid is producedas an impurity along with said acrylic acid, acrylic acid derivatives,or mixtures thereof; and wherein the selectivity of said propionic acidis less than about 5 mol %. In another embodiment of the presentinvention, propionic acid is produced as an impurity along with saidacrylic acid, acrylic acid derivatives, or mixtures thereof; and whereinthe selectivity of said propionic acid is less than about 1 mol %.

In one embodiment of the present invention, said acrylic acid, acrylicacid derivatives, or mixtures thereof are produced with a yield of atleast about 70 mol % and with a selectivity of at least about 70 mol %over a TOS of about 72 h; wherein propionic acid is produced as animpurity along with said acrylic acid, acrylic acid derivatives, ormixtures thereof; and wherein the selectivity of said propionic acid isless than about 5 mol % over said TOS of about 72 h. In anotherembodiment of the present invention, said acrylic acid, acrylic acidderivatives, or mixtures thereof are produced with a yield of at leastabout 80 mol % and with a selectivity of at least about 80 mol % over aTOS of about 72 h; wherein propionic acid is produced as an impurityalong with said acrylic acid, acrylic acid derivatives, or mixturesthereof; and wherein the selectivity of said propionic acid is less thanabout 1 mol % over said TOS of about 72 h.

In one embodiment of the present invention, said acrylic acid, acrylicacid derivatives, or mixtures thereof are produced with a conversion ofsaid hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof of more than about 50 mol %. In another embodiment ofthe present invention, said acrylic acid, acrylic acid derivatives, ormixtures thereof are produced with a conversion of said hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof of morethan about 80 mol %.

In one embodiment of the present invention, acetic acid, pyruvic acid,1,2-propanediol, hydroxyacetone, acrylic acid dimer, and2,3-pentanedione are produced along with said acrylic acid, acrylic acidderivatives, or mixtures thereof with a yield of less than about 2 mol %each. In another embodiment of the present invention, acetic acid,pyruvic acid, 1,2-propanediol, hydroxyacetone, acrylic acid dimer, and2,3-pentanedione are produced along with said acrylic acid, acrylic acidderivatives, or mixtures thereof with a yield of less than about 0.5 mol% each. In yet another embodiment of the present invention, acetaldehydeis produced along with said acrylic acid, acrylic acid derivatives, ormixtures thereof with a yield of less than about 8 mol %. In even yetanother embodiment of the present invention, acetaldehyde is producedalong with said acrylic acid, acrylic acid derivatives, or mixturesthereof with a yield of less than about 4 mol %. In one embodiment ofthe present invention, acetaldehyde is produced along with said acrylicacid, acrylic acid derivatives, or mixtures thereof with a yield of lessthan about 3 mol %.

In one embodiment of the present invention, said phosphate salt iscrystalline; wherein said x is 1; wherein said cation is K⁺; whereinsaid wall material further comprises nickel in an amount between about50 wt % and about 75 wt %, chromium in an amount between about 15 wt %and about 20 wt %, and iron in an amount between about 3 wt % and about30%; wherein said amount of said aluminum is between about 3 wt % andabout 5 wt %; wherein said hydroxypropionic acid is lactic acid; whereinsaid temperature is about 375° C. and said water partial pressure isabout 13 bar; wherein said GHSV is about 2,300 h⁻¹ and said WHSV isbetween about 0.3 h⁻¹ and about 0.4 h⁻¹; wherein said acrylic acid,acrylic acid derivatives, or mixtures thereof are produced with a yieldof at least about 80% and with a selectivity of at least about 80% overa TOS of about 72 h; wherein propionic acid is produced as an impurityalong with said acrylic acid, acrylic acid derivatives, or mixturesthereof; and wherein the selectivity of said propionic acid is less thanabout 1 mol % over said TOS of about 72 h.

In another embodiment of the present invention, said phosphate salt iscrystalline; wherein said x is 1; wherein said cation is Cs⁺; whereinsaid wall material further comprises nickel in an amount between about50 wt % and about 75 wt %, chromium in an amount between about 15 wt %and about 20 wt %, and iron in an amount between about 3 wt % and about30%; wherein said amount of said aluminum is between about 3 wt % andabout 5 wt %; wherein said hydroxypropionic acid is lactic acid; whereinsaid temperature is about 375° C. and said water partial pressure isabout 13 bar; wherein said GHSV is about 2,300 h⁻¹ and said WHSV isbetween about 0.3 h⁻¹ and about 0.4 h⁻¹; wherein said acrylic acid,acrylic acid derivatives, or mixtures thereof are produced with a yieldof at least about 80% and with a selectivity of at least about 80% overa TOS of about 72 h; wherein propionic acid is produced as an impurityalong with said acrylic acid, acrylic acid derivatives, or mixturesthereof; and wherein the selectivity of said propionic acid is less thanabout 1 mol % over said TOS of about 72 h.

In yet another embodiment of the present invention; said phosphate saltis crystalline; wherein said x is 1; wherein said cation is K⁺; whereinsaid wall material further comprises nickel in an amount of about 60 wt%, chromium in an amount between about 20 wt % and about 30 wt %, andiron in an amount between about 3 wt % and about 20 wt %; wherein saidamount of said aluminum is between about 1 wt % and about 4 wt %;wherein said hydroxypropionic acid is lactic acid; wherein saidtemperature is about 375° C. and said water partial pressure is about 13bar; wherein said GHSV is about 2,300 h⁻¹ and said WHSV is between about0.3 h⁻¹ and about 0.4 h⁻¹; wherein said acrylic acid, acrylic acidderivatives, or mixtures thereof are produced with a yield of at leastabout 80% and with a selectivity of at least about 80% over a TOS ofabout 72 h; wherein said acrylic acid, acrylic acid derivatives, ormixtures thereof are produced with a yield of at least about 80 mol %and with a selectivity of at least about 80 mol % over a TOS of about 72h; wherein propionic acid is produced as an impurity along with saidacrylic acid, acrylic acid derivatives, or mixtures thereof; and whereinthe selectivity of said propionic acid is less than about 1 mol % oversaid TOS of about 72 h.

In even yet another embodiment of the present invention; said phosphatesalt is crystalline; wherein said x is 1; wherein said cation is Cs⁺;wherein said wall material further comprises nickel in an amount ofabout 60 wt %, chromium in an amount between about 20 wt % and about 30wt %, and iron in an amount between about 3 wt % and about 20 wt %;wherein said amount of said aluminum is between about 1 wt % and about 4wt %; wherein said hydroxypropionic acid is lactic acid; wherein saidtemperature is about 375° C. and said water partial pressure is about 13bar; wherein said GHSV is about 2,300 h⁻¹ and said WHSV is between about0.3 h⁻¹ and about 0.4 h⁻¹; wherein said acrylic acid, acrylic acidderivatives, or mixtures thereof are produced with a yield of at leastabout 80% and with a selectivity of at least about 80% over a TOS ofabout 72 h; wherein said acrylic acid, acrylic acid derivatives, ormixtures thereof are produced with a yield of at least about 80 mol %and with a selectivity of at least about 80 mol % over a TOS of about 72h; wherein propionic acid is produced as an impurity along with saidacrylic acid, acrylic acid derivatives, or mixtures thereof; and whereinthe selectivity of said propionic acid is less than about 1 mol % oversaid TOS of about 72 h.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprises contactinga gas feed stream comprising water vapor and hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof with a catalystin a single-layer reactor at a temperature, a water partial pressure, aGHSV, and a WHSV to dehydrate said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof; wherein saidcatalyst comprises a phosphate salt comprising a cation and an anionrepresented by the empirical formula [H_(2(1−x))PO_((4−x))]; wherein xis any real number greater than or equal to 0 and less than or equal to1; wherein said water partial pressure is equal to or greater than about0.4 bar; wherein said single-layer reactor comprises a wall, an outersurface, and an inner surface; wherein said wall is made from a wallmaterial, has a wall thickness, and extends from said outer surface tosaid inner surface; wherein said wall material comprises aluminum in anamount greater than about 1 wt %; wherein said inner surface is incontact with said catalyst; wherein said single-layer reactor has acorrosion rate lower than about 1.3 mm/y during said dehydration; andwhereby acrylic acid, acrylic acid derivatives, or mixtures thereof areproduced as a result of said dehydration in said single-layer reactor.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprisescontacting a gas feed stream comprising water vapor and lactic acid,lactic acid derivatives, or mixtures thereof with a catalyst in asingle-layer reactor at a temperature, a water partial pressure, a GHSV,and a WHSV to dehydrate said lactic acid, lactic acid derivatives, ormixtures thereof; wherein said catalyst comprises a phosphate saltcomprising a monovalent cation and an anion represented by the empiricalformula [H_(2(1−x))PO_((4−x)))]⁻; wherein x is any real number greaterthan or equal to 0 and less than or equal to 1; wherein said cation isselected from the group consisting of K⁺, Cs⁺, and mixtures thereof;wherein said temperature is between about 300° C. and about 450° C.;wherein said water partial pressure is equal to or greater than about0.4 bar; wherein said GHSV is about 2,300 h⁻¹; wherein said WHSV isbetween about 0.3 h⁻¹ and about 0.4 h⁻¹; wherein said single-layerreactor comprises a wall, an outer surface, and an inner surface;wherein said wall is made from a wall material, has a wall thickness,and extends from said outer surface to said inner surface; wherein saidwall material comprises aluminum in an amount greater than about 1 wt %;wherein said inner surface is in contact with said catalyst; whereinsaid single-layer reactor has a corrosion rate lower than about 1.3 mm/yduring said dehydration; wherein said acrylic acid, acrylic acidderivatives, or mixtures thereof are produced with a yield of at leastabout 80 mol % and with a selectivity of at least about 80 mol % over aTOS of about 72 h; wherein propionic acid is produced as an impurityalong with said acrylic acid, acrylic acid derivatives, or mixturesthereof; and wherein the selectivity of said propionic acid is less thanabout 1 mol % over said TOS of about 72 h.

In yet another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprisescontacting a gas feed stream comprising water vapor and hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof with acatalyst in a single-layer reactor at a temperature, a water partialpressure, a GHSV, and a WHSV to dehydrate said hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof; wherein saidcatalyst comprises a phosphate salt comprising a cation and an anionrepresented by the empirical formula [H_(2(1−x))PO_((4−x))]⁻; wherein xis any real number greater than or equal to 0 and less than or equal to1; wherein said water partial pressure is equal to or greater than about0.4 bar; wherein said single-layer reactor comprises a wall, an outersurface, and an inner surface; wherein said wall is made from a wallmaterial, has a wall thickness, and extends from said outer surface tosaid inner surface; wherein said wall material comprises silicon in anamount greater than about 1 wt %; wherein said inner surface is incontact with said catalyst; wherein said single-layer reactor has acorrosion rate lower than about 1.3 mm/y during said dehydration; andwhereby acrylic acid, acrylic acid derivatives, or mixtures thereof areproduced as a result of said dehydration in said single-layer reactor.

In even yet another embodiment of the present invention, a method ofmaking acrylic acid, acrylic acid derivatives, or mixtures thereofcomprises contacting a gas feed stream comprising water vapor andhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof with a catalyst in a bi-layer reactor at a temperature, a waterpartial pressure, a GHSV, and a WHSV to dehydrate said hydroxypropionicacid, hydroxypropionic acid derivatives, or mixtures thereof; whereinsaid catalyst comprises a phosphate salt comprising a cation and ananion represented by the empirical formula [H_(2(1−x))PO_((4−x))]⁻;wherein x is any real number greater than or equal to 0 and less than orequal to 1; wherein said water partial pressure is equal to or greaterthan about 0.4 bar; wherein said bi-layer reactor comprises an outerlayer, an inner layer, an outer surface, an inner surface, and aninterface between said outer layer and said inner layer; wherein saidouter layer is made from an outer layer material, has an outer layerthickness, and extends from said interface to said outer surface;wherein said inner layer is made from an inner layer material, has aninner layer thickness, and extends from said inner surface to saidinterface; wherein said inner layer material is selected from the groupconsisting of aluminum, silicon, copper, silver, gold, titanium,tantalum, tungsten, molybdenum, platinum, palladium, zirconium, andmixtures thereof; wherein said inner surface is in contact with saidcatalyst; wherein said bi-layer reactor has a corrosion rate lower thanabout 1.3 mm/y during said dehydration; and whereby acrylic acid,acrylic acid derivatives, or mixtures thereof are produced as a resultof said dehydration in said bi-layer reactor.

In one embodiment of the present invention, said gas feed streamcomprising water vapor and hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof is produced by contacting a liquid feedstream comprising hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof with water vapor. In another embodimentof the present invention, said gas feed stream comprising water vaporand lactic acid, lactic acid derivatives, or mixtures thereof isproduced by contacting a liquid feed stream comprising lactic acid,lactic acid derivatives, or mixtures thereof with water vapor. In yetanother embodiment of the present invention, said liquid feed streamcomprising hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof can further comprise one or more essentially chemicallyinert liquids. Non-limiting examples of essentially chemically inertliquids are water, hydrocarbons, chlorinated hydrocarbons, fluorinatedhydrocarbons, brominated hydrocarbons, esters, ethers, ketones,aldehydes, acids, alcohols, or mixtures thereof. Non-limiting examplesof hydrocarbons are C5 to C8 linear and branched alkanes. A non-limitingexample of esters is ethyl acetate. A non-limiting example of ethers isdiphenyl ether. A non-limiting example of ketones is acetone.Non-limiting examples of alcohols are methanol, ethanol, and C3 to C8linear and branched alcohols. In one embodiment of the presentinvention, said one or more essentially chemically inert liquidscomprise water. In one embodiment of the present invention, said one ormore essentially chemically inert liquids consists essentially of water.

In one embodiment of the present invention, a liquid feed streamcomprising water and hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof is fed into an evaporator upstream ofthe catalytic reactor for the liquid feed stream to become a gas feedstream comprising water vapor and hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof, at leastpartially, before contacting said catalyst. In another embodiment of thepresent invention, a liquid feed stream comprising water andhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof is fed directly into the catalytic reactor and contacted withsaid catalyst. In yet another embodiment of the present invention, anessentially chemically inert gas or an essentially chemically inertliquid is fed into the evaporator or into the catalytic reactor. Theliquid feed stream comprising hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof and the essentially chemicallyinert gas or the essentially chemically inert liquid can be jointly orseparately fed into said evaporator or said catalytic reactor.Non-limiting examples of essentially chemically inert gases arenitrogen, helium, air, argon, carbon dioxide, carbon monoxide, watervapor, and mixtures thereof. Non-limiting examples of essentiallychemically inert liquids are water, hydrocarbons, chlorinatedhydrocarbons, fluorinated hydrocarbons, brominated hydrocarbons, esters,ethers, ketones, aldehydes, acids, alcohols, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprises: a)providing a liquid feed stream comprising hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof; b) optionallycombining said liquid feed stream with an essentially chemically inertgas to form a liquid/gas blend; and c) contacting said liquid feedstream or said liquid/gas blend with any catalyst disclosed in SectionII (“Active Catalysts for the Dehydration of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) or any precursorcatalyst disclosed in Section III (“Precursor Catalysts for theDehydration of Hydroxypropionic Acid or its Derivatives to Acrylic Acidor its Derivatives”) of the present invention under a water partialpressure of about 0.4 bar or more to produce said acrylic acid, acrylicacid derivatives, or mixtures thereof.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprises:a) providing a liquid feed stream comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof; b) optionally combining said liquid feed stream with anessentially chemically inert gas to form a liquid/gas blend; and c)contacting said liquid feed stream or said liquid/gas blend with anycatalyst disclosed in Section II (“Active Catalysts for the Dehydrationof Hydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any precursor catalyst disclosed in Section III(“Precursor Catalysts for the Dehydration of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) of the presentinvention under a water partial pressure of about 0.4 bar or more toproduce said acrylic acid, acrylic acid derivatives, or mixturesthereof.

In yet another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprises:a) providing a liquid feed stream comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof; b) optionally combining said liquid feed stream with anessentially chemically inert gas to form a liquid/gas blend; c)evaporating said liquid feed stream or said liquid/gas blend to producea gas feed stream; and d) contacting said gas feed stream with anycatalyst disclosed in Section II (“Active Catalysts for the Dehydrationof Hydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any precursor catalyst disclosed in Section III(“Precursor Catalysts for the Dehydration of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) of the presentinvention under a water partial pressure of about 0.4 bar or more toproduce said acrylic acid, acrylic acid derivatives, or mixturesthereof.

In even yet another embodiment of the present invention, a method ofmaking acrylic acid, acrylic acid derivatives, or mixtures thereofcomprises: a) providing a liquid feed stream comprising an aqueoussolution of hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof; wherein the hydroxypropionic acid is essentially inmonomeric form in the aqueous solution; b) optionally combining saidliquid feed stream with an essentially chemically inert gas to form aliquid/gas blend; c) evaporating said liquid feed stream or saidliquid/gas blend to produce a gas feed stream; and d) contacting saidgas feed stream with any catalyst disclosed in Section II (“ActiveCatalysts for the Dehydration of Hydroxypropionic Acid or itsDerivatives to Acrylic Acid or its Derivatives”) or any precursorcatalyst disclosed in Section III (“Precursor Catalysts for theDehydration of Hydroxypropionic Acid or its Derivatives to Acrylic Acidor its Derivatives”) of the present invention under a water partialpressure of about 0.4 bar or more to produce said acrylic acid, acrylicacid derivatives, or mixtures thereof.

In one embodiment of the present invention, a method of making acrylicacid, acrylic acid derivatives, or mixtures thereof comprises: a)providing a liquid feed stream comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof; wherein the hydroxypropionic acid is essentially in monomericform in the aqueous solution, and wherein the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof comprise betweenabout 10 wt % and about 25 wt % of the aqueous solution; b) optionallycombining said liquid feed stream with an essentially chemically inertgas to form a liquid/gas blend; c) evaporating said liquid feed streamor said liquid/gas blend to produce a gas feed stream; and d) contactingsaid gas feed stream with any catalyst disclosed in Section II (“ActiveCatalysts for the Dehydration of Hydroxypropionic Acid or itsDerivatives to Acrylic Acid or its Derivatives”) or any precursorcatalyst disclosed in Section III (“Precursor Catalysts for theDehydration of Hydroxypropionic Acid or its Derivatives to Acrylic Acidor its Derivatives”) of the present invention under a water partialpressure of about 0.4 bar or more to produce said acrylic acid, acrylicacid derivatives, or mixtures thereof.

In another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprises:a) providing a liquid feed stream comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof; wherein the hydroxypropionic acid comprises oligomers in theaqueous solution; b) heating said liquid feed stream at a temperaturebetween about 50° C. and about 100° C. to hydrolyze the oligomers of thehydroxypropionic acid and produce a liquid feed stream comprisingmonomeric hydroxypropionic acid; c) optionally combining said liquidfeed stream comprising monomeric hydroxypropionic acid with anessentially chemically inert gas to form a liquid/gas blend; d)evaporating said liquid feed stream comprising monomerichydroxypropionic acid or said liquid/gas blend to produce a gas feedstream; and e) contacting said gas feed stream with any catalystdisclosed in Section II (“Active Catalysts for the Dehydration ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any precursor catalyst disclosed in Section III(“Precursor Catalysts for the Dehydration of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) of the presentinvention under a water partial pressure of about 0.4 bar or more toproduce said acrylic acid, acrylic acid derivatives, or mixturesthereof.

In yet another embodiment of the present invention, a method of makingacrylic acid, acrylic acid derivatives, or mixtures thereof comprises:a) providing a liquid feed stream comprising an aqueous solution ofhydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof; b) optionally combining the liquid feed stream with anessentially chemically inert gas to form a liquid/gas blend; c)evaporating said liquid feed stream or said liquid/gas blend to producea gas feed stream; d) contacting said gas feed stream with any catalystdisclosed in Section II (“Active Catalysts for the Dehydration ofHydroxypropionic Acid or its Derivatives to Acrylic Acid or itsDerivatives”) or any precursor catalyst disclosed in Section III(“Precursor Catalysts for the Dehydration of Hydroxypropionic Acid orits Derivatives to Acrylic Acid or its Derivatives”) of the presentinvention under a water partial pressure of about 0.4 bar or more toproduce an acrylic acid stream; and e) cooling said acrylic acid streamto produce a liquid acrylic acid stream comprising said acrylic acid,acrylic acid derivatives, or mixtures thereof.

In one embodiment of the present invention, the concentration of thehydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof in said liquid feed stream is between about 2 wt % and about 95wt %. In another embodiment of the present invention, the concentrationof the hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof in said liquid feed stream is between about 5 wt % andabout 60 wt %. In yet another embodiment of the present invention, theconcentration of the hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof in said liquid feed stream is betweenabout 10 wt % and about 40 wt %. In even yet another embodiment of thepresent invention, the concentration of the hydroxypropionic acid,hydroxypropionic acid derivatives, or mixtures thereof in said liquidfeed stream is about 20 wt %.

In one embodiment of the present invention, the liquid feed streamcomprises an aqueous solution of hydroxypropionic acid, hydroxypropionicacid derivatives, or mixtures thereof. In another embodiment of thepresent invention, the liquid feed stream comprises an aqueous solutionof lactic acid, lactic acid derivatives, or mixtures thereof. In yetanother embodiment of the present invention, said lactic acidderivatives in said aqueous solution are selected from the groupconsisting of metal or ammonium salts of lactic acid, alkyl esters oflactic acid, lactic acid oligomers, cyclic di-esters of lactic acid,lactic acid anhydride, 2-alkoxypropionic acids or their alkyl esters,2-aryloxypropionic acids or their alkyl esters, 2-acyloxypropionic acidsor their alkyl esters, or a mixture thereof.

In one embodiment of the present invention, the concentration of thelactic acid, lactic acid derivatives, or mixtures thereof in saidaqueous solution is between about 2 wt % and about 95 wt %. In anotherembodiment of the present invention, the concentration of the lacticacid, lactic acid derivatives, or mixtures thereof in said aqueoussolution is between about 5 wt % and about 60 wt %. In yet anotherembodiment of the present invention, the concentration of the lacticacid, lactic acid derivatives, or mixtures thereof in said aqueoussolution is between about 10 wt % and about 40 wt %. In even yet anotherembodiment of the present invention, the concentration of the lacticacid, lactic acid derivatives, or mixtures thereof in said aqueoussolution is about 20 wt %. In one embodiment of the present invention,the liquid feed stream comprises an aqueous solution of lactic acidalong with lactic acid derivatives. In another embodiment of the presentinvention, the liquid feed stream comprises less than about 30 wt % oflactic acid derivatives, based on the total weight of the liquid feedstream. In yet another embodiment of the present invention, the liquidfeed stream comprises less than about 10 wt % of lactic acidderivatives, based on the total weight of the liquid feed stream. Ineven yet another embodiment of the present invention, the liquid feedstream comprises less than about 5 wt % of lactic acid derivatives,based on the total weight of the liquid feed stream.

Lactic acid can be in monomeric form or as oligomers in said aqueoussolution of lactic acid, lactic acid derivatives, or mixtures thereof.In one embodiment of the present invention, the oligomers of the lacticacid in said aqueous solution of lactic acid, lactic acid derivatives,or mixtures thereof are less than about 30 wt % based on the totalamount of lactic acid, lactic acid derivatives, or mixtures thereof. Inanother embodiment of the present invention, the oligomers of the lacticacid in said aqueous solution of lactic acid, lactic acid derivatives,or mixtures thereof are less than about 10 wt % based on the totalamount of lactic acid, lactic acid derivatives, or mixtures thereof. Inyet another embodiment of the present invention, the oligomers of thelactic acid in said aqueous solution of lactic acid, lactic acidderivatives, or mixtures thereof are less than about 5 wt % based on thetotal amount of lactic acid, lactic acid derivatives, or mixturesthereof. In even yet another embodiment of the present invention, thelactic acid is essentially in monomeric form in said aqueous solution oflactic acid, lactic acid derivatives, or mixtures thereof.

The process to remove the oligomers from the aqueous solution of lacticacid, lactic acid derivatives, and mixtures thereof can comprise apurification step or hydrolysis by heating step. In one embodiment ofthe present invention, the heating step can involve heating the aqueoussolution of lactic acid, lactic acid derivatives, or mixtures thereof ata temperature between about 50° C. and about 100° C. to hydrolyze theoligomers of the lactic acid. In another embodiment of the presentinvention, the heating step can involve heating the aqueous solution oflactic acid, lactic acid derivatives, or mixtures thereof at atemperature between about 95° C. and about 100° C. to hydrolyze theoligomers of the lactic acid. In yet another embodiment of the presentinvention, the heating step can involve heating the aqueous solution oflactic acid, lactic acid derivatives, or mixtures thereof at atemperature between about 50° C. and about 100° C. to hydrolyze theoligomers of the lactic acid and produce a monomeric lactic acid aqueoussolution comprising at least 80 wt % of lactic acid in monomeric formbased on the total amount of lactic acid, lactic acid derivatives, ormixtures thereof. In even yet another embodiment of the presentinvention, the heating step can involve heating the aqueous solution oflactic acid, lactic acid derivatives, or mixtures thereof at atemperature between about 50° C. and about 100° C. to hydrolyze theoligomers of the lactic acid and produce a monomeric lactic acid aqueoussolution comprising at least 95 wt % of lactic acid in monomeric formbased on the total amount of lactic acid, lactic acid derivatives, ormixtures thereof. In one embodiment of the present invention, an about88 wt % aqueous solution of lactic acid, lactic acid derivatives, ormixtures thereof is diluted with water and the oligomers are hydrolyzedto produce an aqueous solution of about 20 wt % lactic acid. The lacticacid oligomers can result in loss of acrylic acid selectivity due totheir high boiling point. As the water content decreases in the aqueoussolution, the loss of feed material to the catalyst reaction, due tolosses in the evaporation step, increases. Additionally, lactic acidoligomers can cause coking, catalyst deactivation, and reactor plugging.

In another embodiment of the present invention, the liquid feed streamcomprising hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof can further comprise one or more antioxidants. Inanother embodiment of the present invention, the liquid feed streamcomprising hydroxypropionic acid, hydroxypropionic acid derivatives, ormixtures thereof further comprises butylated hydroxy toluene (BHT),butylated hydroxy anisole (BHA), or mixtures thereof. In yet anotherembodiment of the present invention, the liquid feed stream comprisinghydroxypropionic acid, hydroxypropionic acid derivatives, or mixturesthereof further comprises ethylene glycol, ethanedithiol, methanol,methanethiol, or mixtures thereof.

The liquid feed stream can be introduced into the evaporator or into thecatalytic reactor with a simple tube or through atomization nozzles.Non-limiting examples of atomization nozzles comprise fan nozzles,pressure swirl atomizers, air blast atomizers, two-fluid atomizers,rotary atomizers, and supercritical carbon dioxide atomizers. In oneembodiment of the present invention, the droplets of the aqueoussolution are less than about 500 μm in diameter. In another embodimentof the present invention, the droplets of the aqueous solution are lessthan about 200 μm in diameter. In yet another embodiment of the presentinvention, the droplets of the aqueous solution are less than about 100μm in diameter.

In the evaporation step, said liquid feed stream or said liquid/gasblend are heated to produce a gas feed stream. In one embodiment of thepresent invention, the temperature during the evaporation step isbetween about 165° C. and about 450° C. In another embodiment of thepresent invention, the temperature during the evaporation step isbetween about 200° C. and about 400° C. In yet another embodiment of thepresent invention, the temperature during the evaporation step isbetween about 250° C. and about 375° C. In even yet another embodimentof the present invention, the temperature during the evaporation step isbetween about 300° C. and about 375° C. In one embodiment of the presentinvention, the temperature during the evaporation step is about 250° C.In another embodiment of the present invention, the temperature duringthe evaporation step is about 375° C.

In one embodiment of the present invention, the residence time in theevaporator during said evaporation step is between about 0.2 s and about10 s. In another embodiment of the present invention, the residence timein the evaporator during said evaporation step is between about 0.5 sand about 5 s. In yet another embodiment of the present invention, theresidence time in the evaporator during said evaporation step is betweenabout 1 s and about 3 s. In even yet another embodiment of the presentinvention, the residence time in the evaporator during said evaporationstep is between about 0.5 s and about 0.6 s.

The evaporation step can be performed under vacuum, at atmosphericpressure, or at pressure higher than atmospheric. In one embodiment ofthe present invention, the evaporation step is performed under a totalpressure of at least about 1 bar. In another embodiment of the presentinvention, the evaporation step is performed under a total pressurebetween about 2 bar and about 100 bar. In yet another embodiment of thepresent invention, the evaporation step is performed under a pressurebetween about 5 bar and about 40 bar. In even yet another embodiment ofthe present invention, the evaporation step is performed under a totalpressure between about 10 bar and about 35 bar. In one embodiment of thepresent invention, the evaporation step is performed under a totalpressure of about 1.6 bar. In another one embodiment of the presentinvention, the evaporation step is performed under a total pressure ofabout 8 bar. In yet another embodiment of the present invention, theevaporation step is performed under a total pressure of about 26 bar.

The evaporation step can be performed in various types of evaporators,such as, but not limited to, atomizer, plate heat exchanger, empty flowreactor, and fixed bed flow reactor. The evaporation step can beperformed in an evaporator with the liquid feed stream flowing down, orflowing up, or flowing horizontally. In one embodiment of the presentinvention, the evaporation step is performed in an evaporator with theliquid feed stream flowing down. Also, the evaporation step can be donein a batch form.

In one embodiment of the present invention, the material of theevaporator inner surface is selected from the group consisting ofamorphous silica, quartz, other silicon oxides, borosilicate glass,silicon, and mixtures thereof. In yet another embodiment of the presentinvention, the material of the evaporator inner surface is amorphoussilica or borosilicate glass.

In one embodiment of the present invention, the evaporation anddehydration steps are combined in a single step. In another embodimentof the present invention, the evaporation and dehydration steps areperformed sequentially in a single reactor. In yet another embodiment ofthe present invention, the evaporation and dehydration steps areperformed sequentially in a tandem reactor.

The acrylic acid stream produced in said dehydration is cooled to give aliquid acrylic acid stream as the product stream. The time required tocool the acrylic acid stream must be controlled to reduce acrylic acidpolymerization or decomposition to ethylene. In one embodiment of thepresent invention, the residence time of the acrylic acid stream in thecooling step is less than about 30 s. In another embodiment of thepresent invention, the residence time of the acrylic acid stream in thecooling step is between about 0.1 s and about 10 s.

The liquid acrylic acid stream comprising acrylic acid, acrylic acidderivatives, or mixtures thereof produced according with the presentinvention can be purified using some or all of the processes ofextraction, drying, distilling, cooling, partial melting, and decantingdescribed in US20130274518A1 or US20150329462A1 (incorporated herein byreference) to produce crude and glacial acrylic acid. Afterpurification, the crude and glacial acrylic acid can be polymerized toproduce a superabsorbent polymer using processes that are similar tothose described in US20130274697A1 or US20130273384A1 (incorporatedherein by reference).

In one embodiment of the present invention, said crude acrylic acid isesterified with an alcohol to produce an acrylate monomer. Non-limitingexamples of alcohols are methanol, ethanol, butanol (n-butyl alcohol),2-ethyl hexanol, isobutanol, tert-butyl alcohol, hexyl alcohol, octylalcohol, isooctyl alcohol, lauryl alcohol, propyl alcohol, isopropylalcohol, hydroxyethyl alcohol, hydroxypropyl alcohol, and polyols, suchas hydroxyalkyl and alkylalkanolamine. In another embodiment of thepresent invention, said crude acrylic acid is esterified with methanol,ethanol, n-butyl alcohol, or 2-ethyl hexanol to produce methyl acrylatemonomer, ethyl acrylate monomer, n-butyl acrylate monomer, or2-ethylhexyl acrylate monomer, respectively. In yet another embodimentof the present invention, said methyl acrylate monomer, ethyl acrylatemonomer, n-butyl acrylate monomer, or 2-ethylhexyl acrylate monomer ispolymerized to produce methyl acrylate polymer, ethyl acrylate polymer,n-butyl acrylate polymer, or 2-ethylhexyl acrylate polymer,respectively. In even yet another embodiment of the present invention,said methyl acrylate monomer, ethyl acrylate monomer, n-butyl acrylatemonomer, or 2-ethylhexyl acrylate monomer is co-polymerized with othermonomer to produce methyl acrylate co-polymer, ethyl acrylateco-polymer, n-butyl acrylate co-polymer, or 2-ethylhexyl acrylateco-polymer, respectively. Non-limiting examples of other monomers arevinyl acetate and ethylene. In one embodiment of the present invention,said methyl acrylate polymer, ethyl acrylate polymer, n-butyl acrylatepolymer, or 2-ethylhexyl acrylate polymer is blended with methylmethacrylate (MMA) to produce blends of MMA and methyl acrylate polymer,blends of MMA and ethyl acrylate polymer, blends of MMA and n-butylacrylate polymer, or blends of MMA and 2-ethylhexyl acrylate polymer,respectively. Non-limiting applications of polymers, co-polymers, orblends are in surface coatings, paints, resins, adhesives, plastics, anddispersions. In another embodiment of the present invention, saidalcohol is bio-based alcohol. In yet another embodiment of the presentinvention, said other monomer is bio-based monomer. In even yet anotherembodiment of the present invention, said MMA is bio-based MMA.

In one embodiment of the present invention, a method of making acrylicacid comprises:

-   -   a) diluting an about 88 wt % lactic acid aqueous solution with        water to form an about 20 wt % lactic acid aqueous solution;    -   b) heating the about 20 wt % lactic acid aqueous solution at a        temperature between about 95° C. and about 100° C. to hydrolyze        oligomers of the lactic acid, producing a monomeric lactic acid        solution comprising at least about 95 wt % of the lactic acid in        monomeric form based on the total amount of lactic acid, lactic        acid derivatives, or mixtures thereof;    -   c) combining the monomeric lactic acid solution with nitrogen to        form a liquid/gas blend;    -   d) evaporating the liquid/gas blend in a evaporator with a        residence time between about 0.5 s and about 0.6 s at a        temperature between about 300° C. and about 375° C. to produce a        gas feed stream comprising about 2.5 mol % lactic acid and about        50 mol % water vapor;    -   e) contacting said gas feed stream with any catalyst disclosed        in Section II (“Active Catalysts for the Dehydration of        Hydroxypropionic Acid or its Derivatives to Acrylic Acid or its        Derivatives”) or Section III (“Precursor Catalysts for the        Dehydration of Hydroxypropionic Acid or its Derivatives to        Acrylic Acid or its Derivatives”) of the present invention in a        single-layer reactor at a temperature, a water partial pressure,        a GHSV, and a WHSV to dehydrate said lactic acid and produce an        acrylic acid stream; wherein said water partial pressure is        equal to or greater than about 0.4 bar; wherein said        single-layer reactor comprises a wall, an outer surface, and an        inner surface; wherein said wall is made from a wall material,        has a wall thickness, and extends from said outer surface to        said inner surface; wherein said wall material comprises        aluminum in an amount greater than about 1 wt %; wherein said        inner surface is in contact with said catalyst; wherein said        single-layer reactor has a corrosion rate lower than about 1.3        mm/y during said dehydration; and    -   f) cooling said acrylic acid stream with a residence time        between about 0.1 s and about 10 s to produce said a liquid        acrylic acid stream comprising said acrylic acid.

In another embodiment of the present invention, a method of makingacrylic acid comprises:

-   -   a) diluting an about 88 wt % lactic acid aqueous solution with        water to form an about 20 wt % lactic acid aqueous solution;    -   b) heating the about 20 wt % lactic acid aqueous solution at a        temperature between about 95° C. and about 100° C. to hydrolyze        oligomers of the lactic acid, producing a monomeric lactic acid        solution comprising at least about 95 wt % of the lactic acid in        monomeric form based on the total amount of lactic acid, lactic        acid derivatives, or mixtures thereof;    -   c) combining the monomeric lactic acid solution with nitrogen to        form a liquid/gas blend;    -   d) evaporating the liquid/gas blend in a evaporator with a        residence time between about 0.5 s and about 0.6 s at a        temperature between about 300° C. and about 375° C. to produce a        gas feed stream comprising about 2.5 mol % lactic acid and about        50 mol % water vapor;    -   e) contacting said gas feed stream with a catalyst in a        single-layer reactor at a temperature, a water partial pressure,        a GHSV, and a WHSV to dehydrate said lactic acid and produce an        acrylic acid stream; wherein said catalyst comprises a phosphate        salt CsH_(2(1−x))PO_((4−x)); wherein x is any real number        greater than or equal to 0 and less than or equal to 1; wherein        said single-layer reactor comprises a wall, an outer surface,        and an inner surface; wherein said wall is made from a wall        material, has a wall thickness, and extends from said outer        surface to said inner surface; wherein said wall material        comprises nickel in an amount between about 50 wt % and about 75        wt %, chromium in an amount between about 15 wt % and about 20        wt %, iron in an amount between about 3 wt % and about 30%, and        aluminum in an amount between about 3 wt % and about 5 wt %;        wherein said temperature is about 375° C. and said water partial        pressure is about 13 bar; wherein said GHSV is about 2,300 h⁻¹        and said WHSV is between about 0.3 h⁻¹ and about 0.4 h⁻¹;        wherein said acrylic acid is produced with a yield of at least        about 80 mol % and with a selectivity of at least about 80 mol %        over a TOS of about 72 h; wherein propionic acid is produced as        an impurity along with said acrylic acid; wherein the        selectivity of said propionic acid is less than about 1 mol %        over said TOS of about 72 h; wherein said inner surface is in        contact with said catalyst; and wherein said single-layer        reactor has a corrosion rate lower than about 1.3 mm/y during        said dehydration; and    -   f) cooling said acrylic acid stream with a residence time        between about 0.1 s and about 10 s to produce a liquid acrylic        acid stream comprising said acrylic acid.

In yet another embodiment of the present invention, a method of makingacrylic acid comprises:

-   -   a) diluting an about 88 wt % lactic acid aqueous solution with        water to form an about 20 wt % lactic acid aqueous solution;    -   b) heating the about 20 wt % lactic acid aqueous solution at a        temperature between about 95° C. and about 100° C. to hydrolyze        oligomers of the lactic acid, producing a monomeric lactic acid        solution comprising at least about 95 wt % of the lactic acid in        monomeric form based on the total amount of lactic acid, lactic        acid derivatives, or mixtures thereof;    -   c) combining the monomeric lactic acid solution with nitrogen to        form a liquid/gas blend;    -   d) evaporating the liquid/gas blend in a evaporator with a        residence time between about 0.5 s and about 0.6 s at a        temperature between about 300° C. and about 375° C. to produce a        gas feed stream comprising about 2.5 mol % lactic acid and about        50 mol % water;    -   e) contacting said gas feed stream with a catalyst in a        single-layer reactor at a temperature, a water partial pressure,        a GHSV, and a WHSV to dehydrate said lactic acid and produce an        acrylic acid stream; wherein said catalyst comprises a phosphate        salt KH_(2(1−x))PO_((4−x)); wherein x is any real number greater        than or equal to 0 and less than or equal to 1; wherein said        single-layer reactor comprises a wall, an outer surface, and an        inner surface; wherein said wall is made from a wall material,        has a wall thickness, and extends from said outer surface to        said inner surface; wherein said wall material comprises nickel        in an amount between about 50 wt % and about 75 wt %, chromium        in an amount between about 16 wt % and about 20 wt %, iron in an        amount between about 3 wt % and about 30%, and aluminum in an        amount between about 3 wt % and about 5 wt %; wherein said        temperature is about 375° C. and said water partial pressure is        about 13 bar; wherein said GHSV is about 2,300 h⁻¹ and said WHSV        is between about 0.3 h⁻¹ and about 0.4 h⁻¹; wherein said acrylic        acid is produced in a yield of at least about 80% and with a        selectivity of at least about 80% over a TOS of about 72 h;        wherein propionic acid is produced with a selectivity of less        than about 1% over said TOS of about 72 h; wherein said inner        surface is in contact with said catalyst; and wherein said        single-layer reactor has a corrosion rate lower than about 1.3        mm/y during said dehydration; and    -   f) cooling said acrylic acid stream with a residence time        between about 0.1 s and about 10 s to produce a liquid acrylic        acid stream comprising said acrylic acid.

In even yet another embodiment of the present invention, a method ofmaking acrylic acid comprises:

-   -   a) diluting an about 88 wt % lactic acid aqueous solution with        water to form an about 20 wt % lactic acid aqueous solution;    -   b) heating the about 20 wt % lactic acid aqueous solution at a        temperature between about 95° C. and about 100° C. to hydrolyze        oligomers of the lactic acid, producing a monomeric lactic acid        solution comprising at least about 95 wt % of the lactic acid in        monomeric form based on the total amount of lactic acid, lactic        acid derivatives, or mixtures thereof;    -   c) combining the monomeric lactic acid solution with nitrogen to        form a liquid/gas blend;    -   d) evaporating the liquid/gas blend in a evaporator with a        residence time between about 0.5 s and about 0.6 s at a        temperature between about 300° C. and about 375° C. to produce a        gas feed stream comprising about 2.5 mol % lactic acid and about        50 mol % water vapor;    -   e) contacting said gas feed stream with a catalyst in a bi-layer        reactor at a temperature, a water partial pressure, a GHSV, and        a WHSV to dehydrate said lactic acid and produce an acrylic acid        stream; wherein said catalyst comprises a phosphate salt        KH_(2(1−x))PO_((4−x)); wherein x is any real number greater than        or equal to 0 and less than or equal to 1; wherein said bi-layer        reactor comprises an outer layer, an inner layer, an outer        surface, an inner surface, and an interface between said outer        layer and said inner layer; wherein said outer layer is made        from an outer layer material, has an outer layer thickness, and        extends from said interface to said outer surface; wherein said        inner layer is made from an inner layer material, has an inner        layer thickness, and extends from said inner surface to said        interface; wherein said inner layer material is selected from        the group consisting of aluminum, silicon, and mixtures thereof;        wherein said inner surface is in contact with said catalyst;        wherein said outer layer is selected from the group consisting        of stainless steel and carbon steel; wherein said inner layer is        formed by a dipping process of said outer layer in a bath        comprising said inner layer material; wherein said dipping        process is followed by oxidation of said inner surface; wherein        said temperature is about 375° C. and said water partial        pressure is about 13 bar; wherein said GHSV is about 2,300 h⁻¹        and said WHSV is between about 0.3 h⁻¹ and about 0.4 h⁻¹;        wherein said acrylic acid is produced with a yield of at least        about 80 mol % and with a selectivity of at least about 80 mol %        over a TOS of about 72 h; wherein propionic acid is produced as        an impurity along with said acrylic acid; wherein the        selectivity of said propionic acid is less than about 1 mol %        over said TOS of about 72 h; and wherein said bi-layer reactor        has a corrosion rate lower than about 1.3 mm/y during said        dehydration; and    -   f) cooling said acrylic acid stream with a residence time        between about 0.1 s and about 10 s to produce a liquid acrylic        acid stream comprising said acrylic acid.

VI Examples

The following examples are provided to illustrate the invention, but arenot intended to limit the scope thereof.

Example 1—Precursor Catalyst with 13 wt % KPO₃, 37 wt % Ba₂P₂O₇, and 50%Fused Silica

Barium nitrate (Ba(NO₃)₂ (150.00 g, 550.5 mmol; Sigma-Aldrich Co., St.Louis, Mo.; catalog #202754), dipotassium phosphate K₂HPO₄ (31.96 g,183.5 mmol; Sigma-Aldrich Co., St. Louis, Mo.; catalog #60347), andammonium phosphate dibasic (NH₄)₂HPO₄ (99.21 g, 734.0 mmol;Sigma-Aldrich Co., St. Louis, Mo.; catalog #379980) were combined andground together using a planetary ball mill (Retsch GmbH, Haan, Germany;model PM 100; catalog #20.540.0003) to obtain a fine powder. Then, thematerial was transferred into a 1 L glass beaker and calcined using alab furnace with air circulation (Nabertherm GmbH, Lilienthal, Germany;catalog # N30/85 HA; conditions: 450° C., 12 h, 2° C./min heating ramp,and open exhaust). The calcined solid was ground and sieved to obtain asolid with particle size between 106 μm and 212 μm. Then, 4.18 g of thissolid and 4.18 g of fused silica (Sigma-Aldrich Co., St. Louis, Mo.;catalog #342831; ground and sieved to 106-212 μm) were added to a glassscintillation vial and mixed in a vortex mixer until well blended. Theresulting precursor catalyst contained 13 wt % KPO₃, 37 wt % Ba₂P₂O₇,and 50% Fused Silica.

Example 2—20 wt % Lactic Acid Aqueous Solution

455 g of an 88 wt % L-lactic acid solution (Corbion Purac Co., Lenexa,Kans.) was diluted with 1,508 g of water. The diluted solution washeated to 95° C. and held at that temperature with stirring for about 12hours. Then, the solution was cooled to room temperature, and its lacticacid monomer concentration was measured by an Agilent 1100 HPLC system(Agilent Technologies, Inc., Santa Clara, Calif.) equipped with a DADdetector and an Atlantis T3 column (Waters Corp., Milford, Mass.;Catalog #186003748) using methods generally known by those havingordinary skill in the art to yield a 20 wt % L-lactic acid aqueoussolution and essentially free of oligomers.

Example 3—Testing of Precursor Catalyst

A stainless steel glass-lined tube reactor (SGE Analytical Science PtyLtd., Ringwood, Australia; P/N: 08277028) with 12.7 mm (2 in.) OD, 9.5mm ID, and 60 cm length was packed in 3 zones as follows: 1) bottomzone: 0.4 g of quartz wool, 24.1 g of 4-20 mesh fused silica(Sigma-Aldrich Co., St. Louis, Mo.; catalog #342831), and 0.2 g quartzwool were packed to give a bottom zone length of 30.5 cm (12 in.); 2)middle zone/dehydration zone: 8.81 g of the precursor catalyst preparedin Example 1 were packed to give a catalyst bed length of 10.2 cm (4in.; 7.2 mL catalyst bed volume); and 3) top zone/evaporator zone: 0.1 gof quartz wool was placed on top of the dehydration zone followed by 3.6g of fused silica (4-20 mesh) to give an evaporator zone of 5.1 cm (2in.) in length.

The reactor was first placed inside an aluminum block and then placed ina Series 3210 clam shell furnace (Applied Test Systems, Butler, Pa.)such as the top of the evaporator zone was aligned with the top of thealuminum block. The reactor was set-up in a down-flow arrangement andwas equipped with a Knauer Smartline 100 feed pump (Knauer GmbH, Berlin,Germany), a Brooks 0254 gas flow controller (Brooks Instrument LLC,Hatfield, Pa.), a Brooks back pressure regulator, and a Teflon-linedcatch tank. The head of the reactor was fitted with a 3.2 mm (⅛ in.)stainless steel line, as a nitrogen feed line, and a 1.6 mm ( 1/16 in.)polyetheretherketone (PEEK™) tubing (Supelco Inc., Bellafonte, Pa.), asa liquid feed supply line connected to the feed pump. The bottom of thereactor was connected to the catch tank using a 3.2 mm (⅛ in.) fusedsilica lined stainless steel tubing and Swagelok™ fittings. The clamshell furnace was heated such that the reactor wall temperature was keptconstant at about 375° C. during the course of the reaction.

The reactor was fed with separate liquid and gas feeds, which were mixedtogether before reaching the catalyst bed. The inert gas was nitrogen at24.8 barg (360 psig) pressure and was fed into the reactor at a rate of130 mL/min (under STP conditions). The liquid feed was an aqueoussolution of lactic acid (20 wt % L-lactic acid from Example 2) and wasfed into the reactor at a rate of 0.13 mL/min. After the evaporationzone, the resulting gas feed stream had the following composition: 49.6mol % water, 47.9 mol % nitrogen, and 2.5 mol % lactic acid. In thedehydration zone, the GHSV was about 2,262 h⁻¹, WHSV was about 0.38 h⁻¹,and water partial pressure was about 13 bar (186 psi).

The gas product stream was cooled and analyzed on-line by an Agilent7890A GC (Agilent Technologies, Inc., Santa Clara, Calif.) equipped witha FID detector and Varian CP-PoraBond Q column (Agilent Technologies,Inc., Santa Clara, Calif.; Catalog # CP7351). The liquid product streamwas collected in the catch tank and analyzed off-line (using methodsgenerally known by those having ordinary skill in the art) using anAgilent 1100 HPLC (Agilent Technologies, Inc., Santa Clara, Calif.),equipped with a diode array detector (DAD) and an Atlantis T3 column(Waters Corp., Milford, Mass.; Catalog #186003748), and a HewlettPackard HP6890 series GC (Agilent Technologies, Inc., Santa Clara,Calif.), equipped with an FID detector and Agilent CP-Wax 58 FFAP CBcolumn (Agilent Technologies, Inc., Santa Clara, Calif.; Catalog #CP7717).

The liquid product stream was cooled and collected over a period ofabout 72 h. The overall acrylic acid yield was 84.4 mol %, acrylic acidselectivity was 87.2 mol %, lactic acid conversion was 96.7 mol %, andpropionic acid selectivity was 0.74 mol %.

Comparative Example 4—316L Stainless Steel (316L SS) Coupon

A 316L SS coupon was sanded with emery cloth (320 grit, followed by 500grit) and cleaned with solvent (acetone, hexanes, and then chloroform).The dimensions of the coupon were measured using a micrometer as 30.03mm×8.01 mm×1.5 mm, and the weight of coupon was measured as 2,819.80 mgbefore being placed in the reactor. The nominal chemical composition ofthis alloy includes about 65 wt % iron, about 17 wt % chromium, about 12wt % nickel, and 2-3 wt % molybdenum.

Comparative Example 5—Corrosion Testing of the 316L SS Coupon

A stainless steel glass-lined tube reactor (SGE Analytical Science PtyLtd., Ringwood, Australia; P/N: 08277028) with 12.7 mm (½ in.) OD, 9.5mm ID, and 60 cm length was packed in 3 zones as follows: 1) bottomzone: 0.4 g of quartz wool, 25.15 g of 4-20 mesh fused silica(Sigma-Aldrich Co., St. Louis, Mo.; catalog #342831), and 0.1 g quartzwool were packed to give a bottom zone length of 29.5 cm (11.6 in.); 2)middle zone/dehydration zone: 1.44 g of the precursor catalyst preparedin Example 1 were packed to give a catalyst bed length of 2.54 cm (1in.) at the bottom of this zone, the 316L SS coupon prepared inComparative Example 4 was then placed on top of that precursor catalyst,and then an additional 7.31 g of the precursor catalyst prepared inExample 1 were packed around and on top of the coupon to give a catalystbed of 10.2 cm (4 in.) in total length (a total of 8.75 g of precursorcatalyst mass and 7.2 mL catalyst bed volume); and 3) topzone/evaporator zone: 0.1 g of quartz wool was placed on top of thedehydration zone followed by 3.8 g of fused silica (4-20 mesh) to givean evaporator zone of 5.1 cm (2 in.) in length.

The reactor was first placed inside an aluminum block and then placed ina Series 3210 clam shell furnace (Applied Test Systems, Butler, Pa.)such as the top of the evaporator zone was aligned with the top of thealuminum block. The reactor was set-up in a down-flow arrangement andwas equipped with a Knauer Smartline 100 feed pump (Knauer GmbH, Berlin,Germany), a Brooks 0254 gas flow controller (Brooks Instrument LLC,Hatfield, Pa.), a Brooks back pressure regulator, and a Teflon-linedcatch tank. The head of the reactor was fitted with a 3.2 mm (⅛ in.)stainless steel line, as a nitrogen feed line, and a 1.6 mm ( 1/16 in.)polyetheretherketone (PEEK™) tubing (Supelco Inc., Bellafonte, Pa.), asa liquid feed supply line connected to the feed pump. The bottom of thereactor was connected to the catch tank using a 3.2 mm (⅛ in.) fusedsilica lined stainless steel tubing and Swagelok™ fittings. The clamshell furnace was heated such that the reactor wall temperature was keptconstant at about 375° C. during the course of the reaction.

The reactor was fed with separate liquid and gas feeds, which were mixedtogether before reaching the catalyst bed. The inert gas was nitrogen at24.8 barg (360 psig) pressure and was fed into the reactor at a rate of130 mL/min (under STP conditions). The liquid feed was an aqueoussolution of lactic acid (20 wt % L-lactic acid from Example 2) and wasfed into the reactor at a rate of 0.13 mL/min. After the evaporationzone, the resulting gas feed stream had the following composition: 49.6mol % water, 47.9 mol % nitrogen, and 2.5 mol % lactic acid. In thedehydration zone, the GHSV was about 2,262 h⁻¹, WHSV was about 0.38 h⁻¹,and water partial pressure was about 13 bar (186 psi).

The gas product stream was cooled and analyzed on-line by an Agilent7890A GC (Agilent Technologies, Inc., Santa Clara, Calif.) equipped witha FID detector and Varian CP-PoraBond Q column (Agilent Technologies,Inc., Santa Clara, Calif.; Catalog # CP7351). The liquid product streamwas collected in the catch tank and analyzed off-line (using methodsgenerally known by those having ordinary skill in the art) using anAgilent 1100 HPLC (Agilent Technologies, Inc., Santa Clara, Calif.),equipped with a diode array detector (DAD) and an Atlantis T3 column(Waters Corp., Milford, Mass.; Catalog #186003748), and a HewlettPackard HP6890 series GC (Agilent Technologies, Inc., Santa Clara,Calif.), equipped with an FID detector and Agilent CP-Wax 58 FFAP CBcolumn (Agilent Technologies, Inc., Santa Clara, Calif.; Catalog #CP7717).

The liquid product stream was cooled and collected over a period ofabout 72 h. The overall (i.e., over the 72 h period) acrylic acid yieldwas 81.7 mol %, acrylic acid selectivity was 83.8 mol %, lactic acidconversion was 97.5 mol %, and propionic acid selectivity was 2.02 mol%. At the end of the experiment, the coupon was taken out of thedehydration zone and the corrosion rate was calculated as 3.04 mm/y.

Example 6—Heat-Treated HAYNES® 214® Alloy Coupon

A HAYNES® 214® alloy coupon (Haynes International Inc., Kokomo, Ind.)was sanded with emery cloth (320 grit, followed by 500 grit), cleanedwith solvent (acetone, hexanes, and then chloroform) and heat treated(i.e., oxidized) in a muffle furnace (1 h at 600° C., followed by 1 h at1000° C.; Wilt Industries Inc., Lake Pleasant, N.Y.) before use. Thedimensions of the coupon were measured using a micrometer as 30.38mm×7.97 mm×1.48 mm, and the weight of coupon was measured as 2,768.44 mgbefore being placed in the reactor. The nominal chemical composition ofthis alloy includes about 75 wt % nickel, about 16 wt % chromium, about3 wt % iron, and about 4.5 wt % aluminum. The heat treatment of thecoupon (i.e., the oxidation occurred before the dehydration) aimed atoxidizing the aluminum included in the alloy and forming an oxide-basedsurface passivating layer comprising alumina.

Example 7—Corrosion Testing of the Heat-Treated HAYNES® 214® AlloyCoupon

A stainless steel glass-lined tube reactor (SGE Analytical Science PtyLtd., Ringwood, Australia; P/N: 08277028) with 12.7 mm (½ in.) OD, 9.5mm ID, and 60 cm length was packed in 3 zones as follows: 1) bottomzone: 0.4 g of quartz wool, 25.19 g of 4-20 mesh fused silica(Sigma-Aldrich Co., St. Louis, Mo.; catalog #342831), and 0.1 g quartzwool were packed to give a bottom zone length of 29.5 cm (11.6 in.); 2)middle zone/dehydration zone: 2.18 g of the precursor catalyst preparedin Example 1 were packed to give a catalyst bed length of 2.54 cm (1in.) at the bottom of this zone, the heat-treated HAYNES® 214® alloycoupon prepared in Example 6 was then placed on top of that precursorcatalyst, and then an additional 6.18 g of the precursor catalystprepared in Example 1 were packed around and on top of the coupon togive a catalyst bed of 10.2 cm (4 in.) in total length (a total of 8.36g of precursor catalyst mass and 7.2 mL catalyst bed volume); and 3) topzone/evaporator zone: 0.1 g of quartz wool was placed on top of thedehydration zone followed by 4.32 g of fused silica (4-20 mesh) to givean evaporator zone of 5.1 cm (2 in.) in length.

The reactor was first placed inside an aluminum block and then placed ina Series 3210 clam shell furnace (Applied Test Systems, Butler, Pa.)such as the top of the evaporator zone was aligned with the top of thealuminum block. The reactor was set-up in a down-flow arrangement andwas equipped with a Knauer Smartline 100 feed pump (Knauer GmbH, Berlin,Germany), a Brooks 0254 gas flow controller (Brooks Instrument LLC,Hatfield, Pa.), a Brooks back pressure regulator, and a Teflon-linedcatch tank. The head of the reactor was fitted with a 3.2 mm (⅛ in.)stainless steel line, as a nitrogen feed line, and a 1.6 mm ( 1/16 in.)polyetheretherketone (PEEK™) tubing (Supelco Inc., Bellafonte, Pa.), asa liquid feed supply line connected to the feed pump. The bottom of thereactor was connected to the catch tank using a 3.2 mm (⅛ in.) fusedsilica lined stainless steel tubing and Swagelok™ fittings. The clamshell furnace was heated such that the reactor wall temperature was keptconstant at about 375° C. during the course of the reaction.

The reactor was fed with separate liquid and gas feeds, which were mixedtogether before reaching the catalyst bed. The inert gas was nitrogen at24.8 barg (360 psig) pressure and was fed into the reactor at a rate of130 mL/min (under STP conditions). The liquid feed was an aqueoussolution of lactic acid (20 wt % L-lactic acid from Example 2) and wasfed into the reactor at a rate of 0.13 mL/min. After the evaporationzone, the resulting gas feed stream had the following composition: 49.6mol % water, 47.9 mol % nitrogen, and 2.5 mol % lactic acid. In thedehydration zone, the GHSV was about 2,262 h⁻¹, WHSV was about 0.38 h⁻¹,and water partial pressure was about 13 bar (186 psi).

The gas product stream was cooled and analyzed on-line by an Agilent7890A GC (Agilent Technologies, Inc., Santa Clara, Calif.) equipped witha FID detector and Varian CP-PoraBond Q column (Agilent Technologies,Inc., Santa Clara, Calif.; Catalog # CP7351). The liquid product streamwas collected in the catch tank and analyzed off-line (using methodsgenerally known by those having ordinary skill in the art) using anAgilent 1100 HPLC (Agilent Technologies, Inc., Santa Clara, Calif.),equipped with a diode array detector (DAD) and an Atlantis T3 column(Waters Corp., Milford, Mass.; Catalog #186003748), and a HewlettPackard HP6890 series GC (Agilent Technologies, Inc., Santa Clara,Calif.), equipped with an FID detector and Agilent CP-Wax 58 FFAP CBcolumn (Agilent Technologies, Inc., Santa Clara, Calif.; Catalog #CP7717).

The liquid product stream was cooled and collected over a period ofabout 72 h. The overall (i.e., over the 72 h period) acrylic acid yieldwas 86.2 mol %, acrylic acid selectivity was 88.5 mol %, lactic acidconversion was 97.3 mol %, and propionic acid selectivity was 0.58 mol%. At the end of the experiment, the coupon was taken out of thedehydration zone and the corrosion rate was calculated as 0.79 mm/y.

Example 8—HAYNES® HR-160® Alloy Coupon

A HAYNES® HR-160® alloy coupon (Haynes International Inc., Kokomo, Ind.)was sanded with emery cloth (320 grit, followed by 500 grit) and cleanedwith solvent (acetone, hexanes, and then chloroform) before use. Thedimensions of the coupon were measured using a micrometer as 29.13mm×8.20 mm×1.51 mm, and the weight of coupon was measured as 2,710.33 mgbefore being placed in the reactor. The nominal chemical composition ofthis alloy includes about 37 wt % nickel, about 29 wt % cobalt, about 28wt % chromium, about 2 wt % iron, and about 2.75 wt % silicon. Note thatthe coupon was not heat treated before use (i.e., no oxidation occurredbefore the dehydration), and thus no oxide-based surface passivatinglayer, comprising silica, is expected to have been formed beforedehydration.

Example 9—Corrosion Testing of the HAYNES® HR-160® Alloy Coupon

A stainless steel glass-lined tube reactor (SGE Analytical Science PtyLtd., Ringwood, Australia; P/N: 08277028) with 12.7 mm (½ in.) OD, 9.5mm ID, and 60 cm length was packed in 3 zones as follows: 1) bottomzone: 0.4 g of quartz wool, 24.64 g of 4-20 mesh fused silica(Sigma-Aldrich Co., St. Louis, Mo.; catalog #342831), and 0.1 g quartzwool were packed to give a bottom zone length of 29.5 cm (11.6 in.); 2)middle zone/dehydration zone: 2.41 g of the precursor catalyst preparedin Example 1 were packed to give a catalyst bed length of 2.54 cm (1in.) at the bottom of this zone, the HAYNES® HR-160® coupon prepared inExample 8 was then placed on top of that precursor catalyst, and then anadditional 6.63 g of the precursor catalyst prepared in Example 1 werepacked around and on top of the coupon to give a catalyst bed of 10.2 cm(4 in.) in total length (a total of 9.04 g of precursor catalyst massand 7.2 mL catalyst bed volume); and 3) top zone/evaporator zone: 0.1 gof quartz wool was placed on top of the dehydration zone followed by4.38 g of fused silica (4-20 mesh) to give an evaporator zone of 5.1 cm(2 in.) in length.

The reactor was first placed inside an aluminum block and then placed ina Series 3210 clam shell furnace (Applied Test Systems, Butler, Pa.)such as the top of the evaporator zone was aligned with the top of thealuminum block. The reactor was set-up in a down-flow arrangement andwas equipped with a Knauer Smartline 100 feed pump (Knauer GmbH, Berlin,Germany), a Brooks 0254 gas flow controller (Brooks Instrument LLC,Hatfield, Pa.), a Brooks back pressure regulator, and a Teflon-linedcatch tank. The head of the reactor was fitted with a 3.2 mm (⅛ in.)stainless steel line, as a nitrogen feed line, and a 1.6 mm ( 1/16 in.)polyetheretherketone (PEEK™) tubing (Supelco Inc., Bellafonte, Pa.), asa liquid feed supply line connected to the feed pump. The bottom of thereactor was connected to the catch tank using a 3.2 mm (⅛ in.) fusedsilica lined stainless steel tubing and Swagelok™ fittings. The clamshell furnace was heated such that the reactor wall temperature was keptconstant at about 375° C. during the course of the reaction.

The reactor was fed with separate liquid and gas feeds, which were mixedtogether before reaching the catalyst bed. The inert gas was nitrogen at24.8 barg (360 psig) pressure and was fed into the reactor at a rate of130 mL/min (under STP conditions). The liquid feed was an aqueoussolution of lactic acid (20 wt % L-lactic acid from Example 2) and wasfed into the reactor at a rate of 0.13 mL/min. After the evaporationzone, the resulting gas feed stream had the following composition: 49.6mol % water, 47.9 mol % nitrogen, and 2.5 mol % lactic acid. In thedehydration zone, the GHSV was about 2,262 h⁻¹, WHSV was about 0.38 h⁻¹,and water partial pressure was about 13 bar (186 psi).

The gas product stream was cooled and analyzed on-line by an Agilent7890A GC (Agilent Technologies, Inc., Santa Clara, Calif.) equipped witha FID detector and Varian CP-PoraBond Q column (Agilent Technologies,Inc., Santa Clara, Calif.; Catalog # CP7351). The liquid product streamwas collected in the catch tank and analyzed off-line (using methodsgenerally known by those having ordinary skill in the art) using anAgilent 1100 HPLC (Agilent Technologies, Inc., Santa Clara, Calif.),equipped with a diode array detector (DAD) and an Atlantis T3 column(Waters Corp., Milford, Mass.; Catalog #186003748), and a HewlettPackard HP6890 series GC (Agilent Technologies, Inc., Santa Clara,Calif.), equipped with an FID detector and Agilent CP-Wax 58 FFAP CBcolumn (Agilent Technologies, Inc., Santa Clara, Calif.; Catalog #CP7717).

The liquid product stream was cooled and collected over a period ofabout 72 h. The overall (i.e., over the 72 h period) acrylic acid yieldwas 88 mol %, acrylic acid selectivity was 89.4 mol %, lactic acidconversion was 98.4 mol %, and propionic acid selectivity was 0.42 mol%. At the end of the experiment, the coupon was taken out of thedehydration zone and the corrosion rate was calculated as 1.22 mm/y.

Example 10—Copper Coupon

A copper coupon was sanded with emery cloth (320 grit, followed by 500grit). The dimensions of the coupon were measured using a micrometer as29.46 mm×7.66 mm×1.18 mm, and the weight of coupon was measured as2,400.59 mg before being placed in the reactor.

Example 11—Corrosion Testing of the Copper Coupon

A stainless steel glass-lined tube reactor (SGE Analytical Science PtyLtd., Ringwood, Australia; P/N: 08277028) with 12.7 mm (½ in.) OD, 9.5mm ID, and 60 cm length was packed in 3 zones as follows: 1) bottomzone: 0.4 g of quartz wool, 22.33 g of 4-20 mesh fused silica(Sigma-Aldrich Co., St. Louis, Mo.; catalog #342831), and 0.1 g quartzwool were packed to give a bottom zone length of 29.5 cm (11.6 in.); 2)middle zone/dehydration zone: 2.05 g of the precursor catalyst preparedin Example 1 were packed to give a catalyst bed length of 2.54 cm (1in.) at the bottom of this zone, the copper coupon prepared in Example10 was then placed on top of that precursor catalyst, and then anadditional 5.63 g of the precursor catalyst prepared in Example 1 werepacked around and on top of the coupon to give a catalyst bed of 10.2 cm(4 in.) in total length (a total of 7.68 g of precursor catalyst massand 7.2 mL catalyst bed volume); and 3) top zone/evaporator zone: 0.1 gof quartz wool was placed on top of the dehydration zone followed by3.93 g of fused silica (4-20 mesh) to give an evaporator zone of 5.1 cm(2 in.) in length.

The reactor was first placed inside an aluminum block and then placed ina Series 3210 clam shell furnace (Applied Test Systems, Butler, Pa.)such as the top of the evaporator zone was aligned with the top of thealuminum block. The reactor was set-up in a down-flow arrangement andwas equipped with a Knauer Smartline 100 feed pump (Knauer GmbH, Berlin,Germany), a Brooks 0254 gas flow controller (Brooks Instrument LLC,Hatfield, Pa.), a Brooks back pressure regulator, and a Teflon-linedcatch tank. The head of the reactor was fitted with a 3.2 mm (⅛ in.)stainless steel line, as a nitrogen feed line, and a 1.6 mm ( 1/16 in.)polyetheretherketone (PEEK™) tubing (Supelco Inc., Bellafonte, Pa.), asa liquid feed supply line connected to the feed pump. The bottom of thereactor was connected to the catch tank using a 3.2 mm (⅛ in.) fusedsilica lined stainless steel tubing and Swagelok™ fittings. The clamshell furnace was heated such that the reactor wall temperature was keptconstant at about 375° C. during the course of the reaction.

The reactor was fed with separate liquid and gas feeds, which were mixedtogether before reaching the catalyst bed. The inert gas was nitrogen at24.8 barg (360 psig) pressure and was fed into the reactor at a rate of130 mL/min (under STP conditions). The liquid feed was an aqueoussolution of lactic acid (20 wt % L-lactic acid from Example 2) and wasfed into the reactor at a rate of 0.13 mL/min. After the evaporationzone, the resulting gas feed stream had the following composition: 49.6mol % water, 47.9 mol % nitrogen, and 2.5 mol % lactic acid. In thedehydration zone, the GHSV was about 2,262 h⁻¹, WHSV was about 0.38 h⁻¹,and water partial pressure was about 13 bar (186 psi).

The gas product stream was cooled and analyzed on-line by an Agilent7890A GC (Agilent Technologies, Inc., Santa Clara, Calif.) equipped witha FID detector and Varian CP-PoraBond Q column (Agilent Technologies,Inc., Santa Clara, Calif.; Catalog # CP7351). The liquid product streamwas collected in the catch tank and analyzed off-line (using methodsgenerally known by those having ordinary skill in the art) using anAgilent 1100 HPLC (Agilent Technologies, Inc., Santa Clara, Calif.),equipped with a diode array detector (DAD) and an Atlantis T3 column(Waters Corp., Milford, Mass.; Catalog #186003748), and a HewlettPackard HP6890 series GC (Agilent Technologies, Inc., Santa Clara,Calif.), equipped with an FID detector and Agilent CP-Wax 58 FFAP CBcolumn (Agilent Technologies, Inc., Santa Clara, Calif.; Catalog #CP7717).

The liquid product stream was cooled and collected over a period ofabout 72 h. The overall (i.e., over the 72 h period) acrylic acid yieldwas 86 mol %, acrylic acid selectivity was 88.1 mol %, lactic acidconversion was 97.6 mol %, and propionic acid selectivity was 0.53 mol%. At the end of the experiment, the coupon was taken out of thedehydration zone and no corrosion was observed, so that the corrosionrate was calculated as 0 mm/y.

Tabulated results from the Examples can be seen in Table 1 below.

TABLE 1 Overall Overall Overall Coupon/Corrosion Acrylic Acrylic OverallPropionic Resistant Reactor Acid Acid Lactic Acid Acid Corrosion Example#'s for Metal/Pre-dehydration Yield, Selectivity, Conversion,Selectivity, Rate, Catalyst/Coupon/Testing Oxidation? [mol %] [mol %][mol %] [mol %] [mm/y] Baseline; No/—/— 84.4 87.2 96.7 0.74 — 1/—/3Comparative; 316L SS/—/— 81.7 83.8 97.5 2.02 3.04 1/4/5 Inventive;Heat-treated 86.2 88.5 97.3 0.58 0.79 1/6/7 HAYNES ® 214 ®/Al/YesInventive; HAYNES ® 88 89.4 98.4 0.42 1.22 1/8/9 HR-160 ®/Si/NoInventive; Cu/Cu/No 86 88.1 97.6 0.53 0 1/10/11

The foregoing description is given for clearness of understanding only,and no unnecessary limitations should be understood therefrom, asmodifications within the scope of the invention may be apparent to thosehaving ordinary skill in the art.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests ordiscloses any such invention. Further, to the extent that any meaning ordefinition of a term in this document conflicts with any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A method of making acrylic acid, acrylic acidderivatives, or mixtures thereof comprising contacting a gas feed streamcomprising water vapor and hydroxypropionic acid, hydroxypropionic acidderivatives, or mixtures thereof with a catalyst in a bi-layer reactorat a temperature, a water partial pressure, a GHSV, and a WHSV todehydrate said hydroxypropionic acid, hydroxypropionic acid derivatives,or mixtures thereof, resulting in the production of acrylic acid,acrylic acid derivatives, or mixtures thereof; wherein said catalystcomprises a phosphate salt comprising a cation and an anion representedby the empirical formula:[H_(2(1−x))PO_((4−x))]⁻ wherein x is any real number greater than orequal to 0 and less than or equal to 1; wherein said water partialpressure is equal to or greater than about 0.4 bar; wherein saidbi-layer reactor comprises an outer layer, an inner layer, an outersurface, an inner surface, and an interface between said outer layer andsaid inner layer; wherein said outer layer is made from an outer layermaterial, has an outer layer thickness, and extends from said interfaceto said outer surface; wherein said inner layer is made from an innerlayer material, has an inner layer thickness, and extends from saidinner surface to said interface; wherein said inner layer materialcomprises at least one of aluminum, silicon, or mixtures thereof;wherein said inner surface is in contact with said catalyst; and whereinsaid bi-layer reactor has a corrosion rate lower than about 1.3 mm/yduring said dehydration.
 2. The method of claim 1; wherein saidphosphate salt is crystalline; wherein said x is 0 or 1; and whereinsaid cation is a monovalent cation selected from the group consisting ofK⁺, Cs⁺, and mixtures thereof.
 3. The method of claim 1; wherein saidphosphate salt is amorphous and partially-dehydrated; wherein said x isany real number greater than 0 and less than 1; and wherein said cationis a monovalent cation selected from the group consisting of K⁺, Cs⁺,and mixtures thereof.
 4. The method of claim 1; wherein said outer layercomprises two or more sublayers.
 5. The method of claim 1; wherein saidouter layer material is selected from the group consisting of stainlesssteel and carbon steel.
 6. The method of claim 1; wherein said innerlayer material is selected from the group consisting of aluminum,silicon, and mixtures thereof.
 7. The method of claim 1; wherein saidinner layer is formed by a bonding process of said inner layer to saidouter layer.
 8. The method of claim 7; wherein said bonding process isselected from the group consisting of cladding, laser cladding,explosion cladding, electromagnetic fusion cladding, fusion welding,explosion welding, gluing, pressing, rolling, coextrusion, thermalspraying, electroplating, and chemical vapor deposition.
 9. The methodof claim 8; wherein said bonding process is followed by oxidation ofsaid inner surface when said inner layer material is selected from thegroup consisting of aluminum, silicon, and mixtures thereof.
 10. Themethod of claim 1; wherein said inner layer material is formed by adipping process of said outer layer in a bath comprising said innerlayer material.
 11. The method of claim 10; wherein said dipping processis followed by oxidation of said inner surface when said inner layermaterial is selected from the group consisting of aluminum, silicon andmixtures thereof.
 12. The method of claim 1; wherein said outer layermaterial is stainless steel; wherein said inner layer material is formedby a dipping process of said outer layer in a bath comprising aluminumand silicon; and wherein said inner surface is subjected to oxidationand forms an oxide-based surface passivating layer comprising aluminaand silica.
 13. The method of claim 1; wherein said outer layer materialis stainless steel; wherein said inner layer material is formed by adipping process of said outer layer in a bath comprising aluminum; andwherein said inner surface is subjected to oxidation and forms anoxide-based surface passivating layer comprising alumina.